Metal-Catalyzed Silylene Insertions of Allylic Ethers:  Stereoselective Formation of Chiral Allylic Silanes

Abstract

Silylene insertion into allylic ethers occurs suprafacially to provide enantioenriched allylic silanes and disilanes. Silylene insertion to a variety of protected allylic alcohols utilizing silver- and copper-mediated conditions proved to be a general method for allylic silane formation. Allylic disilanes reacted similarly to allylic silanes, undergoing both annulation and allylation reactions.

Silver‐Catalyzed Silylene Transfer

“…134,135 Since silver-catalyzed di-tert-butylsilylene transfer to Lewis basic carbonyls was established to afford ylides, Woerpel and coworkers investigated the potential of silylene transfer to allylic ethers 197. 136 The resulting oxonium ylide (198) could rearrange through a [2,3]-sila-Wittig rearrangement to afford allylsilane 199 or undergo a [1,2]-Stevens rearrangement to afford allylsilane 200. The latter rearrangement would constitute a formal insertion of silylene into a C--O bond.…”

“…136 The product formation was dependent on the identity of the catalyst. Silver trifluoroacetate promoted the formation of allylic disilane 201, whereas copper(I) triflate catalyzed the formation of allylic silane 202.…”

Silylene Transfer to Allylic Sulfides: Formation of Substituted Silacyclobutanes

“…In contrast to metal-catalyzed silylene insertion reactions with allylic ethers, 17,18 no carbon–sulfur bond insertion products were observed. Instead, the products resulted from formal 1,2-sulfur migration.…”

Silylene oxonium ylides: di-tert-butylsilylene insertion into C–O bonds

“…For reactions that are thought to proceed through oxonium silylene ylide intermediates, [2,3]-sigmatropic products were observed instead of [1,2]-Stevens rearrangement products. Previously, we reported preliminary results of a metal-catalyzed silylene insertion into allylic ethers yielding formal [1,2]-Stevens rearrangement products 16. In this paper, we expand upon the method wherein metal-catalyzed silylene transfer to allylic ethers produces allylic silanes by way of silylene insertion.…”