CYCLOADDITIONS OF METHANE[11]ANNULENONES WITH DICHLORO-KETENES AND CHLORO-KETENES - PREPARATION OF 2H-METHANOCYCLOUNDECA[B]FURAN-2-ONE RING-SYSTEMS

Cycloaddition of dichloroketene with 3,8-methano[11]annulenone 5 proce eded smoothly to give 3-chloro-2H-4,9-methano- and -chloro-2H-6,11-met hano-cycloundeca[b]furan-2-ones 4a and 7a in good combined yield, whil e that with 4,9-methano[11]annulenone 6, gave 3-chloro-2H-5,10-methano cycloundeca[b]furan-2-one 11a in modest yield. Reductive elimination o f the 3-chlorosubstituent of 4a, 7a and 11a was successfully accomplis hed to give the corresponding parent 2H-methanocycloundeca[b]furan-2-o nes 4b, 7b and 11b, respectively. In a similar reaction using chloroke tene, compound 5 gave unsubstituted-, 3-chloroacetyl- and 3-(1-chloroa cetoxy-2-chloro)vinyl- 2H-4,9-methanocycloundeca[b]furan-2-ones 4b, 19 and 20 in good combined yield, while with 6, only oroacetyl-2H-5,10-m ethanocycloundeca[b]furan-2-one 21 was obtained in modest yield. The r eactivity and/or regioselectivity of the cycloadditions were rationali zed on the basis of AM1 calculations. An X-ray crystallographic determ ination of compound 4a was also carried out.