Cycloadditions of methano[11]annulenones with dichloro- and chloro-ketenes. Preparation of 2H-methanocycloundeca[b]furan-2-one ring systems

Cycloaddition of dichloroketene with 3,8-methano[11]annulenone 5 proceeded smoothly to give 3-Chloro-2H-4,9-methano- and 3-Chloro-2H-6,11-methano-cycloundeca[b]furan-2-ones 4a and 7a in good combined yield, while that with 4,9-methano[11]annulenone 6, gave 3-Chloro-2H-5,10-methanocycloundeca[b]furan-2-one 11a in modest yield. Reductive elimination of the 3-chlorosubstituent of 4a, 7a and 11a was successfully accomplished to give the corresponding parent 2H-methanocycloundeca[b]furan-2-ones 4b, 7b and 11b, respectively. In a similar reaction using chloroketene, compound 5 gave unsubstituted-, 3-chloroacetyl- and 3-(1-chloroacetoxy-2-chloro)vinyl-2H-4, 9-methanocycloundeca[b]furan-2-ones 4b, 19 and 20 in good combined yield, while with 6, only 3-chloroacetyl-2H-5,10-methanocycloundeca[b]furan-2-one 21 was obtained in modest yield. The reactivity and/or regioselectivity of the Cycloadditions were rationalized on the basis of AM1 calculations. An X-ray crystallographic determination of compound 4a was also carried out.