MSTFA as an Effective TMS Source for the TMSOTf-Catalzyed Synthesis of Cyclic Acetals.

Commercially and readily available MSTFA [2,2,2-trifluoro- N -methyl- N -(trimethylsilyl)acetamide] was identified as a highly effective TMS (trimethylsilyl) source for the convenient preparation of cyclic acetals under modified Noyori's conditions. The reactions proceeded smoothly under mild conditions, affording a wide range of the corresponding cyclic acetals with excellent yields in the presence of catalytic TMSOTf (trimethylsilyl trifluoromethanesulfonate). The present method does not require a large excess of diols that can be valuable and does not require presynthesized silylated diols. In contrast to other silylating reagents such as BSA [ N , O -bis(trimethylsilyl)acetamide] and BSTFA [ N , O -bis(trimethylsilyl)trifluoroacetamide], the application of MSTFA avoided the inhibition of catalytic acetalization by the side product 2,2,2-trifluoro- N -methylacetamide.