Synthesis and ?-Facially Selective Cycloadditions of Pinofurans

Article abstract of DOI:10.1016/S0040-4020(01)86211-6

The synthesis of the strained pinofuran (1) and methylpinofuran (2) was investigated by a number of approaches.The preferred route to 1 was via the monoprotected (Z)-enediol 8, which was obtained by Z-selective LiNEt2-induced opening of the epoxide derived from protected homoallylic alcohol 3 (nopol).Methylpinofuran (2) was prepared from 1,4-diketone 14, which was obtained by a vinyl-Grignard 1,4-addition to pinocarvone (12) followed by ozonolysis.Pinofurans 1 and 2 entered into Diels-Alder additions with dimethyl acetyenedicarboxylate, giving 15 and 16, respectively.Pinofuran (1) also reacted with allyl cations, giving <4+3> cycloadducts 19 and 20.All cycloadditions were ?-facially selective, attack occurring exclusively from the face anti to the gem-dimethyl grouping.Further, in the case of cycloadduct 19, extended attack was slightly preferred over compact attack (19ββ : 19αα = 3:2) (α, β refer to the tetrahydropyranone moiety).