Furan-2(3H)- and -2(5H)-ones. Part 8.1 Conformation and di-π-methane reactivity of the 4,7-disubstituted tetrahydroisobenzofuran-1-one system: a mechanistic and exploratory study

Abstract

Photoirradiation of cis- and trans-4,7-diphenyl-1,3,4,7-tetrahydroisobenzofuran-1-one cis- and trans-14 and its 4-methyl analogues cis- and trans-15 afford the corresponding di-π-methane rearrangement products 27, 28 and 24 in moderate yields. MM2 calculations for the cis- and trans-4,7-diphenyl substrates cis- and trans-14 showed that the planar structure is most stable for both compounds and that the molecular energy difference between the planar structure and the boat conformation is small enough for a boat–planar–boat conversion. On the basis of the calculations, the di-π-methane rearrangement of the compounds 14 and 15 is supposed to proceed via the boat conformation with a pseudoaxial phenyl substituent. An X-ray structure determination of the two diphenyl substrates cis- and trans-14 provides strong support for the validity of the calculations in predicting optimum structures for cis- and trans-disubstituted tetrahydroisobenzofuranone.