Reactions of 7‐(Methoxyimino)‐4‐methyl‐2H‐chromene‐2,8(7H)‐dione with Phosphorus Ylides. Synthesis of 2‐Substituted 6‐Methyl‐8H‐benzopyrano[7,8‐d]oxazol‐8‐ones

Abstract 7‐(Methoxyimino)‐4‐methyl‐2H‐chromene‐2,8(7H)‐dione (3) reacts with phosphonium salts 1a–c, 8a, b under phasetransfer catalysis conditions to afford the title 2‐substituted 6‐methylbenzopyranooxazol‐8‐ones 5a–c, 10a, b, respectively, along with compound 6, instead of the expected Wittig reaction products. However, the reaction of 3 with the stable phosphorus ylides 11a–c in addition to the corresponding benzopyranooxazoles 12a–c and compound 6 affords in the last case compound 16 as well according to a sequence involving an initial Wittig reaction between 11c and 3.