S(RN)1 reactions of 7-iodobicyclo[4.1.0]heptane, 1-iodoadamantane, and neopentyl iodide with carbanions induced by FeBr2 in DMSO

There was no reaction of 7-iodobicyclo[4.1.0]heptane (7-iodonorcarane, 1) (exo-endo ratio of ca. 1) with acetophenone enolate ions 2 in DMSO at 25 degrees C; however, with the addition of SmI2 or FeBr2 and under the same experimental conditions, the substitution product 3 was obtained in 9% and 72% yields, respectively, with an exo-endo ratio of ca. 16 similar to the product ratio from photostimulated reactions. Thus, it seems that 7-norcaranyl radicals are intermediates of these reactions. With FeBr2 at 60 degrees C the yield of 3 was as high as 90%. Reactions of 1 with the enolate ion of 2-naphthyl methyl ketone 4 induced by FeBr2 gave substitution product 5 in 60% yield (96% of it the exo isomer). In competition experiments, 4 was 1.7 times more reactive than 2, and the anion of nitromethane (7) was 6.5 times more reactive than 2 toward 7-norcaranyl radicals. The reactions of 1-iodoadamantane (9) and neopentyl iodide (11) with carbanion 2 induced by FeBr2 gave the substitution products in 85% and 92% yields, respectively. These observations indicate that all these reactions induced by FeBr2 occur by the S(RN)1 mechanism.