Synthesis of highly functionalized stable heterocyclic phosphorus ylides, cycloaddition reaction between conjugated phosphorus ylides and alkyl propiolates

Protonation of the reactive 1:1 intermediates produced in the reaction betw een triphenylphosphine and dialkyl acetylene-dicarboxylates by 3-chlorotetr ahydrofuran-2,4-dione leads to vinylphosphonium salts, which undergo Michae l addition with the conjugate base of the CH-acid to produce highly functio nalized phosphorus ylides containing a furandione ring systemin excellent y ields. Using alkyl propiolates, the corresponding phosphorus ylides are for med and undergo [4+2] cycloaddition reaction with the alkyl propiolates to produce hitherto unknown furo[2,3-b]pyran ring systems in good yields. (C) 2000 Elsevier Science Ltd. All rights reserved.