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 between triphenylphosphine and dialkyl acetylenedicarboxylates by 3-chlorotetrahydrofuran-2,4-dione leads to vinylphosphonium salts, which undergo Michael addition with the conjugate base of the CH-acid to produce highly functionalized phosphorus ylides containing a furandione ring system in excellent yields. Using alkyl propiolates, the corresponding phosphorus ylides are formed and undergo [4+2] cycloaddition reaction with the alkyl propiolates to produce hitherto unknown furo[2,3-b]pyran ring systems in good yields.