PAPER	Synthesis 2004: 2135-2152   DOI: 10.1055/s-2004-831166
© Georg Thieme Verlag Stuttgart · New York
Stereoselective Preparation of (E)-α-Bromoacrylates from Mixtures of Brominated­ Ando Phosphonates
Thomas Olpp, Reinhard Brückner*
Institut für Organische Chemie und Biochemie, Albert-Ludwigs-Universität, Albertstr. 21, 79104 Freiburg, Germany Fax: +49(761)2036100; e-Mail: reinhard.brueckner@organik.chemie.uni-freiburg.de;
Received 31 March 2004

Abstract

We prepared 69:31-11:89 mixtures of phosphonates 6b and 7b containing two phenoxy substituents, a CO₂Et 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 °C provided unsaturated α-bromoesters. Yields were typically 70-99% and E-selectivities (i.e. ester and β-substituent cis) 80:20-98:2. Similarly, we proceeded via the chlorinated phosphonate 49 to the unsaturated α-chloroester 51 with E:Z = 94:6 (80%).

Key words

α-bromoacrylates - brominated alkenes - α-chloroacrylates - chlorinated alkenes - Horner-Wadsworth-Emmons olefination - α,β-unsaturated esters