3-tert-Butyldimethylsilyloxymethyl-2-lithio-2-phenylsulfonyloxirane as a glycidyl anion equivalent; preparation of terminal epoxy ketones

Abstract

3-tert-Butyldimethylsilyloxymethyl-2-phenylsulfonyloxirane 2 is efficiently substituted at the 2-position by deprotonation followed by quenching with electrophiles to give 2-substituted 2-phenylsulfonyloxiranes 4. These adducts may be converted in a three-step process into epoxy ketones 1 by ring-opening with magnesium bromide to give the α-bromo ketones 9, desilylation with boron trifluoride–diethyl ether to give the bromohydrins 11 and ring-closure with triethylamine to give the epoxy ketones 1. Alternatively, treatment of the α-bromo ketones 9 with tetrabutylammonium fluoride gives the epoxy ketones 1 in a single step. The ring-opening reaction with magnesium bromide and the ring-closure reaction with tetrabutylammonium fluoride may be carried out in a one-pot process. 2-Acylated 2-phenylsulfonyloxiranes are able act as acyl transfer agents both in an inter- and an intra-molecular sense.