Conformational restraint in thermal rearrangements of a cyclobutane:: 3,4-Dicyanotricyclo[4.2.2.02,5]decane

There being no study of a cyclobutane so fused to another cyclic system that an antiperiplanar conformation of the related diradical be precluded, the system in the title has been synthesized and studied for its thermal behavior. In comparison to the thermal behavior of unconstrained 1,2-dicyanocyclobutane in stereomutation and fragmentation to acrylonitrile, the constrained system shows a similar to10-fold higher ratio of stereomutation to fragmentation to the three cis-1,4-bis-beta-cyanovinylcyclohexanes. In these diolefins, a stereochemical correlation between the two olefinic fragmentation products is preserved. Revealed in the thermal rearrangement of isomer trans-1 is a surprising excess (78%) of cis-1-cis-beta-cyanovinyl-4-trans-beta-cyanovinylcyclohexane, cis,trans-2, the result of zero internal rotations within the diradical-in-caldera prior to fragmentation (retention of configuration). Similarly, to a comparably striking extent, anti,cis-l gives trans,trans-2 as its major product (71%), again by zero internal. rotations.