Furan-2(3H)- and -2(5H)-ones. Part 6. Di-π-methane rearrangement of the α-substituted 4-benzylfuran-2(5H)-one system

Abstract

The effect of the ‘central methane’ substitution on the di-π-methane rearrangement in 4-benzyl-2,5-dihydrofuran-2-ones 8a–d was investigated. Significant enhancement of efficiency in the rearrangement leading in high combined yields to two isomeric products, endo-12 and exo-12, is discussed in terms of both the substituent effects at the benzylic carbon and the restrained features of the ring-enrolled π-system. The origin of the difference in chemoselectivity compared with that of the 3-benzyl counterpart 5 where a photoarylated product 6 resulted upon photoirradiation was also investigated, and was rationalized by postulating a higher reactivity at the β-position of the enone system.