Enantioselective iminium-catalyzed epoxidation of hindered trisubstituted allylic alcohols
摘要:
The reactivity of diastereomeric biaryl iminium cations made of a (Ra)-5,5',6,6',7,7',8,8'-octahydrobinaphthyl core and exocyclic appendages derived from (S)- or (R)-3,3-dimethylbutyl-2-amine was investigated with hindered trisubstituted allylic alcohols a class of alkenes which had not been previously studied in detail in epoxidation reactions with cyclic iminium catalysts (ee up to 98%). Surprisingly, generally strong matched/mismatched effects are observed not only in terms of reactivity but also on the enantioselectivity of the reaction (Ace up to 16%). Also, for the most hindered substrates, two sets of reaction conditions were tested in a preliminary study and little advantage was found in running reactions in MeCN/water instead of CH(2)Cl(2)/water/18-C-6. In any case, the presence of the hydroxyl group did not reveal any anchimeric effect. (C) 2010 Elsevier Ltd. All rights reserved.
One-step base promoted strategy for cyanation of α,α-diaryl alcohols has been developed under mild and transition metal-free conditions. This method provides a straightforward and facile way towards the synthesis of β,γ-unsaturated nitriles and α-phenylnitiriles from α-vinyl carbinols and α,α-diaryl methanols, respectively, up to 99% yield. Moreover, various azides and ethers could also be accessed