The Homoconjugated Electron-Releasing Carbonyl Group of 1-Methylbicyclo[2.2.1]hept-5-en-2-one. Regioselective syntheses of 5-chloro- and 6-chloro-1-methylbicyclo[2.2.1]hept-5-en-2-one

Syntheses of (±)-2-exo-cyano-1-methyl-7-oxabicyclo2.2.1]hept-5-en-2-endo-yl acetate ( 1 ) and of (±)-1-methyl-7-oxabicyclo2.2.1]hept-5-en-2-one ( 2 ) are reported. The additon of PhSeCl to 1 afforded (±)-5-endo-chloro-2-exo-cyano-1-methyl-6-exo-(phenylselenenyl)-7-oxabicyclo2.2.1]hept-2-endo-yl acetate ( 6 ), whereas 2 added to PhSeCl with the opposite regioselectivity giving (±)-6-endo-chloro-1-methyl-5-exo-(phenylselenenyl)-7-oxabicyclo2.2.1]heptan-2-one ( 7 ). These adducts were converted into 5-chloro-1-methyl-7-oxabicyclo2.2.1]hept-5-en-2-one ( 9 ) and 6-chloro-1-methyl-7-oxabicyclo2.2.1]hept-5-en-2-one ( 10 ), respectively.