Stereoselective preparation of (E)-α-bromoacrylates from mixtures of brominated ando phosphonates

We prepared 69:31-11:89 mixtures of phosphonates 6b and 7b containing two phenoxy substituents, a CO2 Et group, and 1 or 2 bromine atoms, respectively, at the interspersed methylene group. Deprotonating 64:36 mixtures of these reagents with NaH and adding a variety of aldehydes at 0 degreesC provided unsaturated alpha-bromoesters. Yields were typically 70-99% and E-selectivities (i.e. ester and beta-substituent cis) 80:20-98:2. Similarly, we proceeded via the chlorinated phosphonate 49 to the unsaturated alpha-chloroester 51 with E:Z = 94:6 (80%).