Synthesis of pyrone carbaldehydes, pyrone sulfonium ylides and related epoxides

Hexaminium salts of 4‐pyrones 3a , 3b were synthesized by treatment of 2‐(4‐bromomethylphenyl)‐6‐methyl‐4 H ‐pyran‐4‐one 2a and 2‐(4‐bromomethylphenyl)‐6‐phenyl‐4 H ‐pyran‐4‐one 2b with hexamethyl‐enetetramine in chloroform in 71 and 84% yields respectively. Hydrolysis of 3a and 3b in EtOH:H 2 O produced the corresponding aldehydes 4a and 4b in 43 and 58% yields respectively. The reaction of bromopyrones 2b and 2c with dimethylsulfide in MeOH: CH 2 Cl 2 afforded the corresponding sulfonium salts 5b and 5c in 66 and 65% yields respectively. Treatment of 5b and 5c with arene carbaldehydes such as (Ar = p ‐ClC 6 H 4 , o ‐ClC 6 H 4 , p ‐NO 2 C 6 H 4 , o ‐NO 2 C 6 H 4 , p ‐FC 6 H 4 , 2‐naphthyl, p ‐MeOC 6 H 4 , C 6 H 5 CHCH, p ‐MeC 6 H 4 , C 6 H 5 and 4‐(4‐oxo‐6‐phenyl‐4 H ‐pyran‐2‐yl)‐benzaldehyde 4b ) in the presence of sodium hydroxide in CH 3 CN:H 2 O afforded eleven trans ‐epoxides in 61–93% yields. J. Heterocyclic Chem., 46 , 268 (2009).