Abstract
The silyl-Prins cyclization of geminal vinylsilyl alcohols and aldehydes, promoted by TMSOTf, provides access to polysubstituted tetrahydropyrans in which the silyl group remains in the molecule and an aryl group has migrated from silicon to carbon. This domino silyl-Prins/aryl migration process is general and high-yielding for aryl, vinyl, or alkyl aldehydes. Moreover, cyclization proceeds with very high stereocontrol in a one-pot reaction in which both quaternary and tertiary stereogenic centers have been created.
Highlights
The silyl-Prins cyclization of geminal vinylsilyl alcohols and aldehydes, promoted by TMSOTf, provides access to polysubstituted tetrahydropyrans in which the silyl group remains in the molecule and an aryl group has migrated from silicon to carbon
The process typically involves the reaction of homoallylic alcohols with aldehydes in the presence of an acid to provide intermediate tetrahydropyranyl cations, which are trapped by nucleophiles
The alternative use of vinylsilanes in this process has been much less developed, it has effectively been applied to the synthesis of dihydropyrans,[3,4] starting from (Z)vinylsilyl homoallylic alcohols
Summary
5e + 6 (45)c,d aInverse addition: the alcohol is added to a solution of the aldehyde and catalyst in DCM. bThe ratio of products was determined by a 1H NMR (400 MHz) analysis of the crude mixture. cThe Prins and the Cope products could not be separated. dSmall amounts of benzaldehyde were observed in the reaction mixture. eConversion. fThe coalescence of signals in the H NMR spectrum of the Prins and the Cope products made it impossible to measure the ratio. BThe ratio of products was determined by a 1H NMR (400 MHz) analysis of the crude mixture. FThe coalescence of signals in the H NMR spectrum of the Prins and the Cope products made it impossible to measure the ratio. Mechanism of the Oxonia-Cope Rearrangement nature of the aldehyde employed and on the use or not of an excess of aldehyde. The use of alkylic aldehydes or an excess of the corresponding arylic or vinylic aldehydes gives the Prins product almost exclusively or in a very predominant manner. The process is general and high-yielding for alkylic alcohols and a variety of aldehydes. When a benzylic alcohol is used in the process, an oxonia-Cope rearrangement competes with the direct cyclization, whose occurrence is dependent on the Accession Codes
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