A Novel Stereoselective Reaction Cascade Leading fromα-Silylated Allylic Alcohols to Aldol-Type Products
摘要:
The treatment of alpha-silylated allylic alcohols with epoxidizing reagents afforded in a highly stereocontrolled fashion a-silylated aldols. The transformation is proposed to proceed either by a reaction cascade involving stereospecific epoxidation of the allylic-alcohol moiety followed by an acid-supported pinacol-type rearrangement, or by a sequence consisting of a pi-face-selective electrophilic attack at the allylic silane moiety with hyperconjugative stabilization of the evolving carbocation, followed by rearrangement of the thus obtained pentacoordinated silanium ion (see Scheme 3). Depending on the reaction conditions, the pi-face selectivity of the oxidation step is controlled by the: stereogenic C-atom or the more remote Si-center of chirality.
A Novel Stereoselective Reaction Cascade Leading fromα-Silylated Allylic Alcohols to Aldol-Type Products
摘要:
The treatment of alpha-silylated allylic alcohols with epoxidizing reagents afforded in a highly stereocontrolled fashion a-silylated aldols. The transformation is proposed to proceed either by a reaction cascade involving stereospecific epoxidation of the allylic-alcohol moiety followed by an acid-supported pinacol-type rearrangement, or by a sequence consisting of a pi-face-selective electrophilic attack at the allylic silane moiety with hyperconjugative stabilization of the evolving carbocation, followed by rearrangement of the thus obtained pentacoordinated silanium ion (see Scheme 3). Depending on the reaction conditions, the pi-face selectivity of the oxidation step is controlled by the: stereogenic C-atom or the more remote Si-center of chirality.
The treatment of alpha-silylated allylic alcohols with epoxidizing reagents afforded in a highly stereocontrolled fashion a-silylated aldols. The transformation is proposed to proceed either by a reaction cascade involving stereospecific epoxidation of the allylic-alcohol moiety followed by an acid-supported pinacol-type rearrangement, or by a sequence consisting of a pi-face-selective electrophilic attack at the allylic silane moiety with hyperconjugative stabilization of the evolving carbocation, followed by rearrangement of the thus obtained pentacoordinated silanium ion (see Scheme 3). Depending on the reaction conditions, the pi-face selectivity of the oxidation step is controlled by the: stereogenic C-atom or the more remote Si-center of chirality.