Photochemical Synthesis and Some Reactions of 7-Oxa- and 7-Thiatricyclo3,6>octan-2-ones

Article abstract of DOI:10.1002/hlca.19920750518

Irradiation (λ=350 nm) of newly synthesized 2-acetyl- or 2-methyl-2-(alk-2-enyl)furan-3(2H)-ones 1 and 2-acetyl- or 2-methyl-2-(prop-2-enyl)thiophen-3(2H)-ones 2 affords the corresponding 1-acetyl- or 1-methyl-substituted 7-oxa- and 7-thiatricyclo<3.2.1.0^3,6>octan-2-ones 10 and 11, respectively, via regioselective intramolecular <2+2> photocycloaddition in 65-95percent yield (Scheme 2).The 1-acetyl-substituted O-derivatives 10b and 10c undergo ring opening on treatment with MeONa in MeOH at -78 deg C to afford stereoselectively methyl 3-exo-acetyl-2-oxabicyclo<3.2.0>heptane-7-endo-carboxylates 12b and 12c, respectively, while a 2:1 diastereomeric mixture of methyl 3-acetyl-2-thiabicyclo<3.2.0>heptane-7-endo-carboxylates 13 and 14 is obtained from the corresponding S-derivative 11b.The outcome of the Huang-Minlon reduction of the 1-methyl-substituted ketones 10a and 11a is again influenced by the heteroatom in the tricycle.While 1-methyl-7-oxatricyclo<3.2.1.0^3,6>octane (15) is the only product from the corresponding oxatricyclooctanone 10a, a 1:2 mixture of 1-methyl-7-thiatricyclo<3.2.1.0^3,6>octane (16) and 3-methylbicyclo<3.1.1>hept-2-ene-6-endo-thiol (17) is obtained from the analogous S-compound 11a, both products stemming from a common carbanion precursor.