S(RN)1 REACTIONS OF 7-IODOBICYCLO[4.1.0]HEPTANE WITH CARBANIONS - A NOVEL STEREOSELECTIVE C-C BOND FORMATION ON CYCLOPROPANE RINGS

The photostimulated reaction of 7-iodobicyclo[4.1.0]-heptane (7-iodono rcarane, 1, a mixture of ca. 1:1 of the exo:endo isomers) with acetoph enone enolate ion 2 in DMSO at 60 degrees C gave the substitution prod ucts 3a (exo) and 3b (endo) in 87% yield (with an exo:endo ratio of 16 ). In the dark at 60 degrees C, not only the ipso substitution product s 3a and 3b (51%), but also the cine substitution product 4 were forme d (20%) by an elimination-addition reaction. In the dark and at room t emperature there is no reaction. It is suggested that 1 reacts with 2 by a photostimulated as well as a thermal (60 degrees C) S(RN)1 reacti on to give the ipso products 3, with a 3a:3b ratio of ca. 15-23, showi ng a stereoselectivity of the 7-norcaranyl radicals in the coupling re action with 2. More selectivity of 1 and 2 was found in the photostimu lated reaction in liquid ammonia (at -33 degrees C), with a 3a:3b rati o of ca. 55, although in lower yields (37%). The photostimulated react ion of 1 with 2-acetonaphthone 7 gave only the ipso products (with an exo:endo ratio of 45) and in dark conditions at 60 degrees C there is no reaction with 7. There was no photostimulated reaction of 1 with th e anion of nitromethane 9 in DMSO. However, the photostimulated reacti on of 1 with 9 in presence of acetone enolate ion 10, the ipso substit ution products derived from 9 were formed (entrainment S(RN)1 reaction ), with an exo:endo ratio of ca. 7.3. From competition experiments, 9 was ca. 6.4 times more reaction than 2.