Benzoyldiisopropylchlorosilane: a visible light photocleavable alcohol protecting group

Abstract

Silyl chlorides are highly valuable and popular reagents for the protection of alcohols. In this edge article we introduce a photocleavable alcohol protecting group on the basis of acyl silanes. To achieve this, acylchlorosilanes that represent a new class of acylsilanes were developed. They can be easily synthesized in a concise sequence of three steps in high overall yield. Alcohol silyl protection takes place under established mild conditions, akin to those associated with classical silicon-based protecting groups. The removal of the Si-group is achieved at room temperature through exposure to visible light (456 nm) in methanol. We demonstrate a broad spectrum of substrates with remarkable tolerance toward diverse functional groups, highlighting a substantial level of orthogonality with respect to other protecting groups. Furthermore, we showcase the robustness of this approach against various transformations.

Scheme 1. Alkyl/arylchlorosilanes as classical alcohol protecting groups and aryldialkylchlorosilanes as their photoactive congeners.

Scheme 2. Synthesis of the chlorosilane 1a and alcohol protection. ^aReaction carried out using 1a (1.5 equiv.) and AgOTf (1.2 equiv.).

Scheme 3. Scope. Yields for deprotection were determined by GC analysis. ^aReaction carried out in acetone/methanol (4 : 1). ^bReaction carried out using 1.5 equiv. of BDIPSCl and 1.2 equiv. of Ag(OTf). ^cReaction carried out in methanol. ^dIsolated yield. ^eReaction carried out under reflux. ^fReaction carried out in DMF.

Scheme 4. Compatibility of the BDIPS-ethers with two different chemical transformations.

Scheme 5. Desilylative rearrangement of benzyl and allyl BDIPS-ethers.