Kazuhiko Takai

Last updated
Kazuhiko Takai
BornDecember 18, 1954
Tokyo, Japan
NationalityJapanese
Alma materKyoto University
Known forTakai–Utimoto olefination Nozaki–Hiyama–Takai–Kishi reaction
AwardsChemical Society of Japan Progress Award (1989)

The Society of Synthetic Organic Chemistry of Japan Award (2008) Chemical Society of Japan Award (2013)

The Society of Synthetic Organic Chemistry of Japan Award (2019)

Contents

Scientific career
FieldsOrganic Chemistry Organometallic Chemistry
Thesis Research on synthetic reactions using amphoteric reactors with aluminum as the key atom  (1983)
Doctoral advisor Hitosi Nozaki
Website https://web.archive.org/web/20240619001159/http://achem.okayama-u.ac.jp/omc/

Kazuhiko Takai (born December 18, 1954) is a professor emeritus of applied chemistry at Okayama University and is the recipient of the 2013 Chemical Society of Japan Award for his work on the use of catalytic metals in synthesis reactions. [1] He studied at Kyoto University with Hitosi Nozaki and at the University of California, Berkeley with Clayton Heathcock. [2] While he is best known for the eponymous Takai olefination, his career has covered a wide variety of topics, including geminal organometallics, organotantalum chemistry, reactions of platinum-group catalysts, and the applications of group 7 metals in organic synthesis.

Career

Takai attended Kyoto University, receiving his Bachelor of Engineering degree in 1977 and Master of Engineering degree in 1979 before pursuing a doctoral degree. Working under Hitosi Nozaki, Takai developed a method for the methylenation of enolizable ketones and aldehydes using geminal dizinc species. [3]

Olefination of ketones and aldehydes via geminal dizinc reagents. ACS Takai Nozaki.svg
Olefination of ketones and aldehydes via geminal dizinc reagents.

After focusing on the role of organoaluminium compounds in cross-couplings, [4] sigmatropic rearrangements, [5] and ketone synthesis, [6] Takai left the doctoral program in 1981 and accepted an assistant professor position in Nozaki's lab. Following completion of his thesis in 1983, Takai joined Clayton Heathcock's lab at the University of California, Berkeley, where he focused on the diastereoselective synthesis of pentane-1,2,3,4-tetraols. [7]

Takai would return to Kyoto and continue working as an assistant professor with Nozaki until his retirement in 1985, where he continued as an assistant professor under Kiichiro Utimoto until 1994. Takai moved to Okayama University to accept an associate professor position, gaining full professorship in 1998. Professor Takai continued his research at Okayama until his retirement in 2022.

Major contributions

The Nozaki–Hiyama–Takai–Kishi Reaction

General mechanism for the NHTK coupling between a vinyl halide and an aldehyde. Nozaki-Hiyama-Takai-Kishi mechanism.svg
General mechanism for the NHTK coupling between a vinyl halide and an aldehyde.

While working as an assistant professor for Nozaki, Takai published several reports describing reactions between unsaturated organohalides and aldehydes in the presence of chromium(II) chloride. [8] While the seminal report boasted mild reaction conditions and broad functional group tolerance, reproducibility issues hampered wide-scale application. The culprit behind the reproducibility issues was outlined in simultaneous publications from Takai [9] and Yoshito Kishi, [10] where they highlighted the importance of catalytic nickel for successful couplings. Several batches of commercial CrCl2 revealed the presence of trace nickel impurities in lower quality samples. It is now accepted that the reaction proceeds via the initial formation of an organonickel species which undergoes transmetallation to the active organochromium nucleophile. This mechanism should not be confused with the related Nozaki–Hiyama allylation, where allylchromium species add into an aldehyde without any nickel additives. [11]

Owing to its mild conditions and broad functional-group tolerance, the NHTK reaction has found applications in several natural product syntheses. One particularly notable example is in Kishi's total synthesis of halichondrin B, where extensive application of the coupling was eventually adapted by Eisai into an industrial route for the FDA-approved anti-cancer drug eribulin. [12]

Structures of halichondrin B (left) and eribulin (right) with bonds made by NHTK couplings highlighted in red. NHTK Eribulin.svg
Structures of halichondrin B (left) and eribulin (right) with bonds made by NHTK couplings highlighted in red.

Olefination reactions

Titanium-mediated olefinations

Takai's proposed catalytic cycle for the olefination of carbonyls with zinc and lead. ACS Zinc-Lead Mech corrected1.svg
Takai's proposed catalytic cycle for the olefination of carbonyls with zinc and lead.

In 1987, Takai reported the synthesis of enol ethers via the olefination of esters. [13] Building on previous studies with Nozaki, these transformations were hypothesized to involve a geminal dizinc intermediate. However, variable yields and reaction times dissuaded wide application of the method, and Lombardo would soon report an alternative procedure that involved "aging" the organozinc intermediate for several days, in what is now known as the Lombardo methylenation. [14] Analysis of several batches of commercial zinc revealed that zinc produced via the pyrometallurgical process contained trace impurities of lead, which significantly altered the outcome of the methylenation. Takai subsequently reported that the methylenation proceeded quickly and reproducibly when catalytic PbCl2 was added to the reaction. It is believed that the mechanism involves formation of a α-iodozinc species which can rapidly transmetallate to the organolead, which then primes the system for a second oxidative addition into the remaining halide. [15] Due to the similarities between Takai and Lombardo's conditions, this general transformation is often referred to as the Takai–Oshima–Lombardo methylenation. [16]

Olefination of carbonyl compounds using a Zn/Pb/Ti system. ACS Zn-Pb olefination scheme.svg
Olefination of carbonyl compounds using a Zn/Pb/Ti system.

Chromium(II)-mediated olefinations

Isolated geminal dichromium species from Takai (top) alongside Anwander and Wener (bottom) ACS Takai Olefination isolated species.svg
Isolated geminal dichromium species from Takai (top) alongside Anwander and Wener (bottom)

While attempting to synthesize geminal trichromium species from iodoform, Takai observed formation of (E)-iodostyrene when benzaldehyde was reacted with CrCl2 and iodoform. [17] This observation led to the development of what is now known as the Takai–Utimoto olefination, where carbonyls can be converted to (E)-haloalkenes in the presence of CrCl2 and the corresponding trihalide. [8] Like the corresponding organozinc reactions, the mechanism was hypothesized to involve a geminal dichromium intermediate, but the existence of such species was not proven until publications from Takai in 2017 alongside Anwander and Werner in 2018. [18] [19] However, unlike earlier zinc reactions, the Takai olefination exhibits a strong preference for the (E)-haloalkene, most likely due to stereoelectronic effects directly prior to oxygen elimination.

Proposed mechanism for the Takai-Utimoto olefination. ACS Takai Olefination mechanism.svg
Proposed mechanism for the Takai–Utimoto olefination.

The formed haloalkenes are versatile synthetic intermediates that can be subjected to one-pot reaction conditions to rapidly build complex systems. One example was reported by Takai, where aldehydes can be subjected to tandem Takai–Utimoto/NHTK conditions to synthesize homologated allylic alcohols in decent yields. [8] Later publications also report substituting the third iodide for heteroatoms or alkanes, allowing for the convenient synthesis of diverse (E)-substituted alkenes. [20] [21]

Modifications to the Takai-Utimoto olefination reported by Takai and coworkers ACS Takai Olefination further examples colors.svg
Modifications to the Takai–Utimoto olefination reported by Takai and coworkers

Organotantalum chemistry

In 1990, Takai and coworkers reported the partial reduction of alkynes to (Z)-olefins in the presence of TaCl5 and zinc. [22] While the initial report involved protodemetallation of the intermediate metallocyclopropene, Takai published a series of subsequent reports that demonstrated the versatility of the organotantalum intermediate. By varying which trapping electrophile is added, a wide variety of functionalities can be synthesized. Notable examples include the synthesis of 1,4-dienes, [23] (E)-allylic hydrazines, [24] polysubstituted furans, [25] (E)-allylic alcohols, [26] and 1-naphthols. [27] While these reactions generally proceed with favorable yields, varying levels of regioselectivity have hindered widespread use.

Abridged reactivity of tantalum-derived metallocyclopropenes. ACS organotantalum revised.svg
Abridged reactivity of tantalum-derived metallocyclopropenes.

Group 7 organometallics

Takai's group has also contributed to the development of group 7 catalysis, mainly focusing on organomanganese and organorhenium-based methods. [28] Primarily focusing on bromotricarbonylrhenium(I) species, Takai demonstrated that these complexes are capable catalysts in a variety of transformations, highlighting their use as agents for C–H and C–C bond activation. Notably, these complexes were capable of forming stereodefined cyclopentenes, [29] inserting terminal alkynes into β-ketoesters, [30] [31] [32] enabling the deaminative annulation of imines to form subsitued indenes, [33] and facilitating a variety of metal-mediated cycloadditions to form fused aromatic species. [34] [35] [32]

Selected reactions of [ReBr(CO)3(THF)2]2 as reported by Takai. ACS rhenium.svg
Selected reactions of [ReBr(CO)3(THF)2]2 as reported by Takai.

While not catalytic, Takai and coworkers developed mild conditions for the activation of manganese powder, allowing for its application as a single electron reductant in several reactions. Despite possessing a stronger reduction potential than zinc, [36] manganese metal was seldom used as a reductant due to its propensity of rapidly forming an oxide coating, and activated forms of the element were most commonly encountered as a Rieke metal. [37] In 1996, Takai reported that commercial manganese was readily activated in the presence of trimethylsilyl chloride and catalytic PbCl2. [38] The activated manganese was a competent reductant and was capable of affecting Barbier allylations and Reformatsky-type reactions.

Selected applications of activated manganese reported by Takai and coworkers. ACS manganese.svg
Selected applications of activated manganese reported by Takai and coworkers.


While Mn(0) is capable of reducing Pb(II), these reactions do not proceed solely in the presence of lead powder. The activated manganese was later shown to serve as a versatile reductant, capable of promoting 3-component couplings, [39] cycloadditions, [40] and cyclopropanations, among other reactions. [41]

References

  1. ↑ "Development of Novel Synthetic Organic Reactions by the Use of Group 4-7 Metals". Chemical Society of Japan. September 11, 2014. Retrieved 2020-11-03.
  2. ↑ "Kazuhiko Takai". Okayama University Department of Applied Chemistry. Retrieved 2020-11-03.
  3. ↑ Takai, Kazuhiko; Hotta, Yuji; Oshima, Koichiro; Nozaki, Hitosi (1978-01-01). "Effective methods of carbonyl methylenation using CH2I2-Zn-Me3Al and CH2Br2-Zn-TiCl4 system" . Tetrahedron Letters. 19 (27): 2417–2420. doi:10.1016/S0040-4039(01)94789-6. ISSN   0040-4039.
  4. ↑ Takai, Kazuhiko; Oshima, Koichiro; Nozaki, Hitosi (1980-01-01). "Carboncarbon bond formation by cross-coupling of enol phosphates with organoaluminium compounds catalyzed by palladium(O) complex" . Tetrahedron Letters. 21 (26): 2531–2534. doi:10.1016/0040-4039(80)80120-1. ISSN   0040-4039.
  5. ↑ Takai, Kazuhiko; Mori, Ichiro; Oshima, Koichiro; Nozaki, Hitosi (1981-01-01). "Aliphatic claisen rearrangement promoted by organoaluminium compounds" . Tetrahedron Letters. 22 (40): 3985–3988. doi:10.1016/S0040-4039(01)82044-X. ISSN   0040-4039.
  6. ↑ Takai, Kazuhiko; Oshima, Koichiro; Nozaki, Hitosi (1981-04-01). "Ketone Synthesis from Acid Chloride by Means of Organometallic Reagent Derived from R3Al–Cu(acac)2-PPh3 System" . Bulletin of the Chemical Society of Japan. 54 (4): 1281–1282. doi:10.1246/bcsj.54.1281. ISSN   0009-2673.
  7. ↑ Takai, Kazuhiko; Heathcock, Clayton H. (1985-09-01). "Acyclic stereoselection. 32. Synthesis and characterization of the diastereomeric (4S)-pentane-1,2,3,4-tetraols" . The Journal of Organic Chemistry. 50 (18): 3247–3251. doi:10.1021/jo00218a001. ISSN   0022-3263.
  8. 1 2 3 Takai, Kazuhiko; Kimura, Keizo; Kuroda, Tooru; Hiyama, Tamejiro; Nozaki, Hitosi (1983-01-01). "Selective grignard-type carbonyl addition of alkenyl halides mediated by chromium(II) chloride" . Tetrahedron Letters. 24 (47): 5281–5284. doi:10.1016/S0040-4039(00)88417-8. ISSN   0040-4039.
  9. ↑ Takai, K.; Tagashira, M.; Kuroda, T.; Oshima, K.; Utimoto, K.; Nozaki, H. (1986-09-01). "Reactions of alkenylchromium reagents prepared from alkenyl trifluoromethanesulfonates (triflates) with chromium(II) chloride under nickel catalysis" . Journal of the American Chemical Society. 108 (19): 6048–6050. doi:10.1021/ja00279a068. ISSN   0002-7863.
  10. ↑ Jin, Haolun.; Uenishi, Junichi.; Christ, William J.; Kishi, Yoshito. (1986-09-01). "Catalytic effect of nickel(II) chloride and palladium(II) acetate on chromium(II)-mediated coupling reaction of iodo olefins with aldehydes" . Journal of the American Chemical Society. 108 (18): 5644–5646. doi:10.1021/ja00278a057. ISSN   0002-7863.
  11. ↑ Okude, Yoshitaka; Hirano, Shigeo; Hiyama, Tamejiro; Nozaki, Hitosi (1977-04-01). "Grignard-type carbonyl addition of allyl halides by means of chromous salt. A chemospecific synthesis of homoallyl alcohols" . Journal of the American Chemical Society. 99 (9): 3179–3181. doi:10.1021/ja00451a061. ISSN   0002-7863.
  12. ↑ Kim, Dae-Shik; Dong, Cheng-Guo; Kim, Joseph T.; Guo, Haibing; Huang, Jian; Tiseni, Paolo S.; Kishi, Yoshito (2009-11-04). "New Syntheses of E7389 C14−C35 and Halichondrin C14−C38 Building Blocks: Double-Inversion Approach" . Journal of the American Chemical Society. 131 (43): 15636–15641. doi:10.1021/ja9058475. ISSN   0002-7863.
  13. ↑ Okazoe, Takashi; Takai, Kazuhiko; Oshima, Koichiro; Utimoto, Kiitiro (1987-09-01). "Alkylidenation of ester carbonyl groups by means of a reagent derived from RCHBr2, Zn, TiCl4, and TMEDA. Stereoselective preparation of (Z)-alkenyl ethers" . The Journal of Organic Chemistry. 52 (19): 4410–4412. doi:10.1021/jo00228a055. ISSN   0022-3263.
  14. ↑ Lombardo, Luciano (1982-01-01). "Methylenation of carbonyl compounds with ZnCH2Br2TiCl4. Application to gibberellins" . Tetrahedron Letters. 23 (41): 4293–4296. doi:10.1016/S0040-4039(00)88728-6. ISSN   0040-4039.
  15. ↑ Takai, Kazuhiko; Kakiuchi, Tadahiro; Kataoka, Yasutaka; Utimoto, Kiitiro (1994-05-01). "A Novel Catalytic Effect of Lead on the Reduction of a Zinc Carbenoid with Zinc Metal Leading to a Geminal Dizinc Compound. Acceleration of the Wittig-Type Olefination with the RCHX2-TiCl4-Zn Systems by Addition of Lead" . The Journal of Organic Chemistry. 59 (10): 2668–2670. doi:10.1021/jo00089a002. ISSN   0022-3263.
  16. ↑ "The Takai–Oshima–Lombardo Methylenation of Carbonyl Compounds". Synfacts. 20 (04): 0391. April 2024. doi:10.1055/s-0043-1773176. ISSN   1861-1958.
  17. ↑ Takai, Kazuhiko (2015-11-15). "Trace Amounts of Second Metal Elements Can Play a Key Role in the Generation of Organometallic Compounds" . Bulletin of the Chemical Society of Japan. 88 (11): 1511–1529. doi:10.1246/bcsj.20150170. ISSN   0009-2673.
  18. ↑ Murai, Masahito; Taniguchi, Ryuji; Hosokawa, Naoki; Nishida, Yusuke; Mimachi, Hiroko; Oshiki, Toshiyuki; Takai, Kazuhiko (2017-09-20). "Structural Characterization and Unique Catalytic Performance of Silyl-Group-Substituted Geminal Dichromiomethane Complexes Stabilized with a Diamine Ligand" . Journal of the American Chemical Society. 139 (37): 13184–13192. doi:10.1021/jacs.7b07487. ISSN   0002-7863.
  19. ↑ Werner, Daniel; Anwander, Reiner (2018-10-31). "Unveiling the Takai Olefination Reagent via Tris(tert-butoxy)siloxy Variants" . Journal of the American Chemical Society. 140 (43): 14334–14341. doi:10.1021/jacs.8b08739. ISSN   0002-7863.
  20. ↑ Takai, Kazuhiko; Kataoka, Yasutaka; Okazoe, Takashi; Utimoto, Kiitiro (1987-01-01). "Stereoselective synthesis of (E)-alkenylsilanes from aldehydes with a reagent prepared by chromium(II) reduction of Me3SiCHBr2" . Tetrahedron Letters. 28 (13): 1443–1446. doi:10.1016/S0040-4039(00)95949-5. ISSN   0040-4039.
  21. ↑ Takai, Kazuhiko; Shinomiya, Norio; Kaihara, Hiroya; Yoshida, Naomi; Moriwake, Toshio; Utimoto, Kiitiro (September 1995). "Transformation of Aldehydes into (E)-1-Alkenylboronic Esters with a Geminal Dichromium Reagent Derived from a Dichloromethylboronic Ester and CrCl2" . Synlett. 1995 (09): 963–964. doi:10.1055/s-1995-5141.
  22. ↑ Kataoka, Yasutaka; Takai, Kazuhiko; Oshima, Koichiro; Utimoto, Kiitiro (1990-01-01). "Reduction of acetylenes to (Z)-olefins by means of low-valent niobium or tantalum" . Tetrahedron Letters. 31 (3): 365–368. doi:10.1016/S0040-4039(00)94556-8. ISSN   0040-4039.
  23. ↑ Takai, Kazuhiko; Yamada, Masashi; Odaka, Hidetoshi; Utimoto, Kiitiro; Fujii, Takeshi; Furukawa, Isao (1995-04-01). "Formal Hydroallylation of Carbon-Carbon Triple Bonds via Tantalum-Alkyne Complexes. Stereoselective Preparation of 1,4-Dienes" . Chemistry Letters. 24 (4): 315–316. doi:10.1246/cl.1995.315. ISSN   0366-7022.
  24. ↑ Takai, Kazuhiko; Miwatashi, Seiji; Kataoka, Yasutaka; Utimoto, Kiitiro (1992-01-01). "Reaction of Tantalum-Alkyne Complexes with Hydrazones. Stereoselective Synthesis of (E)-Allylic Hydrazines" . Chemistry Letters. 21 (1): 99–102. doi:10.1246/cl.1992.99. ISSN   0366-7022.
  25. ↑ Takai, Kazuhiko; Tezuka, Makoto; Kataoka, Yasutaka; Utimoto, Kiitiro (1990-09-01). "Regioselective synthesis of highly substituted furans via tantalum-alkyne complexes" . The Journal of Organic Chemistry. 55 (19): 5310–5312. doi:10.1021/jo00306a005. ISSN   0022-3263.
  26. ↑ Kataoka, Yasutaka; Miyai, Jiro; Oshima, Koichiro; Takai, Kazuhiko; Utimoto, Kiitiro (1992-03-01). "Reactions between tantalum- or niobium-alkyne complexes and carbonyl compounds" . The Journal of Organic Chemistry. 57 (7): 1973–1981. doi:10.1021/jo00033a015. ISSN   0022-3263.
  27. ↑ Kataoka, Yasutaka; Miyai, Jiro; Tezuka, Makoto; Takai, Kazuhiko; Oshima, Koichiro; Utimoto, Kiitiro (1990-01-01). "Preparation of 1-naphthols from acetylenes and o-phthalaldehyde using low-valent tantalum and niobium" . Tetrahedron Letters. 31 (3): 369–372. doi:10.1016/S0040-4039(00)94557-X. ISSN   0040-4039.
  28. ↑ Kuninobu, Yoichiro; Takai, Kazuhiko (2012-06-15). "Development of Novel and Highly Efficient Methods to Construct Carbon–Carbon Bonds Using Group 7 Transition-Metal Catalysts" . Bulletin of the Chemical Society of Japan. 85 (6): 656–671. doi:10.1246/bcsj.20120015. ISSN   0009-2673.
  29. ↑ Yudha S., Salprima; Kuninobu, Yoichiro; Takai, Kazuhiko (2008). "Rhenium-Catalyzed Synthesis of Stereodefined Cyclopentenes from β-Ketoesters and Aliphatic Allenes" . Angewandte Chemie International Edition. 47 (48): 9318–9321. doi:10.1002/anie.200803350. ISSN   1521-3773.
  30. ↑ Kuninobu, Yoichiro; Kawata, Atsushi; Nishi, Mitsumi; Takata, Hisatsugu; Takai, Kazuhiko (2008-12-21). "Rhenium- and manganese-catalyzed insertion of acetylenes into β-keto esters: synthesis of 2-pyranones" . Chemical Communications (47): 6360–6362. doi:10.1039/B814694B. ISSN   1364-548X.
  31. ↑ Kuninobu, Yoichiro; Kawata, Atsushi; Yudha, Salprima S.; Takata, Hisatsugu; Nishi, Mitsumi; Takai, Kazuhiko (2010-05-06). "Rhenium- and manganese-catalyzed carbon–carbon bond formation using 1,3-dicarbonyl compounds and alkynes". Pure and Applied Chemistry (in German). 82 (7): 1491–1501. doi:10.1351/PAC-CON-09-09-21. ISSN   1365-3075.
  32. 1 2 Kuninobu, Yoichiro; Nishi, Mitsumi; Kawata, Atsushi; Takata, Hisatsugu; Hanatani, Yumi; Salprima, Yudha S.; Iwai, Aya; Takai, Kazuhiko (2010-01-15). "Rhenium- and Manganese-Catalyzed Synthesis of Aromatic Compounds from 1,3-Dicarbonyl Compounds and Alkynes" . The Journal of Organic Chemistry. 75 (2): 334–341. doi:10.1021/jo902072q. ISSN   0022-3263.
  33. ↑ Kuninobu, Yoichiro; Nishina, Yuta; Kawata, Atsushi; Shouho, Makoto; Takai, Kazuhiko (2008-01-01). "Rhenium-catalyzed synthesis of indene derivatives via C-H bond activation". Pure and Applied Chemistry. 80 (5): 1149–1154. doi:10.1351/pac200880051149. ISSN   1365-3075.
  34. ↑ Murai, Masahito; Yamamoto, Masaki; Takai, Kazuhiko (2019-05-03). "Rhenium-Catalyzed Regioselective ortho-Alkenylation and [3 + 2 + 1] Cycloaddition of Phenols with Internal Alkynes" . Organic Letters. 21 (9): 3441–3445. doi:10.1021/acs.orglett.9b01214. ISSN   1523-7060.
  35. ↑ Kuninobu, Yoichiro; Yu, Peng; Takai, Kazuhiko (2007-09-05). "Rhenium-catalyzed [2+2] Cycloadditions of Norbornenes with Internal and Terminal Acetylenes" . Chemistry Letters. 36 (9): 1162–1163. doi:10.1246/cl.2007.1162. ISSN   0366-7022.
  36. ↑ "P1: Standard Reduction Potentials by Element". Chemistry LibreTexts. 2013-12-02. Retrieved 2025-06-11.
  37. ↑ Kim, Seung-Hoi; Hanson, Mark V.; Rieke, Reuben D. (1996-03-25). "Direct formation of organomanganese bromides using rieke manganese" . Tetrahedron Letters. 37 (13): 2197–2200. doi:10.1016/0040-4039(96)00258-4. ISSN   0040-4039.
  38. ↑ Takai, Kazuhiko; Ueda, Takashi; Hayashi, Takaki; Moriwake, Toshio (1996-09-23). "Activation of manganese metal by a catalytic amount of PbCl2 and Me3SiCl" . Tetrahedron Letters. 37 (39): 7049–7052. doi:10.1016/0040-4039(96)01548-1. ISSN   0040-4039.
  39. ↑ Takai, Kazuhiko; Ueda, Takashi; Ikeda, Norihiko; Moriwake, Toshio (1996-11-15). "Sequential Generation and Utilization of Radical and Anionic Species with a Novel Manganese−Lead Reducing Agent. Three-Component Coupling Reactions of Alkyl Iodides, Electron-Deficient Olefins, and Carbonyl Compounds" . The Journal of Organic Chemistry. 61 (23): 7990–7991. doi:10.1021/jo9617530. ISSN   0022-3263.
  40. ↑ Takai, Kazuhiko; Kaihara, Hiroya; Higashiura, Ken-ichi; Ikeda, Norihiko (1997-12-01). "Generation of Nonstabilized Carbonyl Ylides with a Manganese−Lead Reducing System and Their [3 + 2] Cycloaddition Reactions" . The Journal of Organic Chemistry. 62 (25): 8612–8613. doi:10.1021/jo971421a. ISSN   0022-3263.
  41. ↑ Takai, Kazuhiko (2002). "Activation of Manganese Metal with a Catalytic Amount of Lead and Me3SiCl and Its Application to Organic Synthesis". 有機合成化学協会誌. 60 (11): 1055–1062. doi:10.5059/yukigoseikyokaishi.60.1055.
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