ChemInform Abstract: Photochemical Synthesis and Some Reactions of 7-Oxa- and 7- Thiatricyclo(3.2.1.03,6)octan-2-ones.

Abstract

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[3.2.1.03,6]octan-2-ones 10 and 11, respectively, via regioselective intramolecular [2 + 2] photocycloaddition in 65–95% yield (Scheme 2). The 1-acetyl-substituted O-derivatives 10b and 10c undergo ring opening on treatment with MeONa in MeOH at–78° to afford stereoselectively methyl 3-exo-acetyl-2-oxabicyclo[3.2.0]heptane-7-endo-carboxylates 12b and 12c, respectively, while a 2:1 diastereoisomeric 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[3.2.1.03,6]-octane (15) is the only product from the corresponding oxatricyclooctanone 10a, a 1:2 mixture of 1-methyl-7-thiatricyclo[3.2.1.03,6]-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.