4-Phosphoranylidenebutenolide intermediates in the synthesis of 4-ylidenebutenolides and 4-ylidenetetronic acids. Synthesis of alkylidenephthalide constituents of celery odour and models for freelingyne

Abstract

The application of 4-phosphoranylidenebutenolides in the synthesis of 4-ylidenebutenolides and 4-ylidenetetronic acid derivatives is examined. 3-Triphenylphosphoranylidenephthalide (11) reacts stereospecifically with aliphatic aldehydes to product (E)-alkylidenephthalides [e.g.(13)] and this work has led to the stereocontrolled synthesis of the odorous alkylidenephthalide constituents (4a and b) of celery. By using the ylide (11), the 3-phenacylidenephthalide (14) and the isomeric phthalides (15) and (17) were synthesised.

Condensations of the phosphoranylidenebutenolides (20b) and (26) with aromatic aldehydes have led to the corresponding isomeric arylmethylenebutenolides (27) and (28), and (29) and (30), respectively. Similarly, compounds (20a) and (11) with the 2-furyl-enynal (32) produced the polyunsaturated ylidenebutenolides (33) and (34), and (35) and (36), respectively; these studies have provided a basis for the development of a synthesis of the sesquiterpene freelingyne (2).