Complete Control of Regioselectivity in the Intramolecular [2 + 2] Photocycloaddition of 2-Alkenyl-3(2<i>H</i>)-furanones by the Length of the Side Chain
The 2-(omega-alkenyl)-substituted 2-methyl-3(2H)-furanones 2a and 2b were prepared from biacetyl (3) in four reaction steps and in overall yields of 20% and 21%, respectively. They underwent a clean intramolecular [2 + 2] photocycloaddition upon irradiation at lambda = 350 nm. Whereas compound 2a reacted in the expected manner and yielded 7-oxabicyclo[3.2.1.0(3,6)]octane 7 (87% yield), the regioselectivity
Photochemical Synthesis and Some Reactions of 7-Oxa-and 7-Thiatricyclo[3.2.1.03,6]octan-2-ones
作者:Rolf-Christoph Gebel、Paul Margaretha
DOI:10.1002/hlca.19920750518
日期:1992.8.13
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