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Asymmetric Diels–Alder Reactions with Chiral Acetylenic Carbene Complexes as Dienophiles

✍ Scribed by Annette Rahm; Arnold L. Rheingold; William D. Wulff

Publisher
Elsevier Science
Year
2000
Tongue
French
Weight
267 KB
Volume
56
Category
Article
ISSN
0040-4020

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✦ Synopsis

AbstractÐA new synthetic method is developed for the asymmetric Diels±Alder reactions of acetylenic dienophiles. Acetylenic Fischer carbene complexes with chiral pyrrolidines as the heteroatom stabilizing substituent were anticipated to block three of the four possible approaches of a diene and lead to selective asymmetric cycloadditions. A series of complexes of the type (CO) 5 MvC((C 4 H 7 N)CR 2 OMe)-CuCH (MCr, W; RH, Me, Ph) were prepared by aminolysis of the corresponding methoxy complexes that have the terminal acetylene protected as a silane. Michael addition is completely suppressed if the alkyne is protected as a triisopropylsilyl group and after aminolylsis by 1,2-addition of a pyrrolidine the terminal alkynyl carbene complexes can be obtained predominately as E-isomers upon protodesilylation. The cycloadditions of the E-isomers (but not Z-isomers) of these complexes occur with signi®cant asymmetric induction with 2-triisopropylsiloxy-1,3-pentadiene (66±73% de) but not with cyclopentadiene and a-triisopropylsiloxyvinyl cyclohexene. A model is presented to account for the observed stereoselectivities.

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ChemInform Abstract: Asymmetric Diels—Al
ChemInform Abstract: Asymmetric Diels—Alder Reactions with Chiral Acetylenic Carbene Complexes as Dienophiles.
✍ Annette Rahm; Arnold L. Rheingold; William D. Wulff 📂 Article 📅 2000 🏛 John Wiley and Sons ⚖ 30 KB 👁 2 views

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