Reversal of Diastereoselectivities in Intra- and Intermolecular Reactions of 2-Adamantanylidenes Primarily Caused by Electron-Donating and Electron- Withdrawing Substituents on C5
摘要:
A reversal of diastereoselectivity was observed for novel 5-(trimethylsilyl)adamantan-2-ylidene (1c) with regard to 5-hydroxyadamantan-2-ylidene (1a). Ostensibly in intermolecular reactions, 5-substituted 2-adamantanylidenes (1) are sterically unbiased. However, inductive effects originating from the pendant group bend the divalent carbon bridge of 1 either toward (ERG's, e.g., -Si(CH3)(3)) or away from (EWG's, e.g., -OH) the gamma-position. Hence, the more exposed side is more susceptible to intermolecular reaction and the other side concomitantly undergoes intramolecular 1,3-CH insertions more readily.
2<i>H</i>-Azirines from a Concerted Addition of Alkylcarbenes to Nitrile Groups
作者:Wolfgang Knoll、Jean-Luc Mieusset、Vladimir B. Arion、Lothar Brecker、Udo H. Brinker
DOI:10.1021/ol100703r
日期:2010.5.21
Photolysis of aziadamantanos in the presence of fumoronitrile (FN) unexpectedly afforded conjugated 2H-azirines resulting from addition of the carbene to the CN triple bond. This represents the first example of a direct azirine formation starting from an alkylcarbene for which a concerted pathway is postulated. The novel outcome if the reaction is favored by the prior formation of a carbene-alkene complex, a type of adduct that only recently has been described.