Apparent carbon-carbon bond cleavage in an epoxide. 2,3,4,5,6-Hexachloro-12-oxopentacyclo[5.4.1.1.8,11.03,10.05,9]tridecane; a minor product from the acid treatment of endrin

The treatment of endrin ( 1 ) with sulfuric acid produces ketoendrin 2 and from 6 to 8% of another product that we show to be 2,3,4,4,5,6-hexachloro-12-oxapentacyclo[5.4.1.1. 8,11 .0 3,10 .0 5,9 ]tridecane 3 , based initially on spectral evidence and confirmed by a single crystal X-ray diffraction study. The formation of 3 involves an apparent and unusual carbon-carbon single bond cleavage in an epoxide accompanied by cycloaddition to a proximate carbon-carbon double bond. This transformation probably proceeds by the route outlined in ref. 1. Some of the observed nmr parameters of 3 are discussed in the light of its structure and a comparison is made with the observed spectra for endrin ( 1 ).