4-Aryl-2 -furanone, formation

Reduction of 3,5,5-tris-aryl-2(5// )-furanones 115 (R, R, R = aryl) with dimethyl sulfide-borane led to the formation of the 2,5-dihydrofurans 116 in high yields. However, in the case of 3,4-diaryl-2(5//)-furanones 115 (R, R = aryl R = H or r = H R, R = aryl), the reduction led to a complicated mixture of products of which only the diarylfurans 117 could be characterized (Scheme 36) (88S68). It was concluded that the smooth conversion of the tris-aryl-2(5//)-furanones to the corresponding furan derivatives with the dimethylsulfide-borane complex in high yields could be due to the presence of bulky aryl substituents which prevent addition reaction across the double bond (88S68). 

Wirth and coworkers have demonstrated that an unsaturated acid 28 reacts with [bis (trifluoroacetoxy)iodo] benzene in the presence of TMSOTf to produce a furanone 34 (Scheme 11) [10]. The combination of the two reagents generates the highly active iodine(III) species PhI(OTf)2 in situ. One proposed mechanism for this remarkable transformation involves the formation of a cationic intermediate 30, which interacts with the aryl moiety represented by the intermediate 31. This aryl substituent then migrates to produce the tertiary cation 32, which in turn interacts with the vicinal hydrogen to furnish the observed furanone 34. 

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