Cyclobutylmethyl radicals

Rate constants for ring-opening of cyclobutylmethyl radicals and anions... 

This reaction is particularly interesting when the intermediate radical adduct rearranges or forms a new carbon-carbon bond. In Eq. (35), ring opening of a cyclobutylmethyl radical derived from -pinene 116 gives the cyclohexene derivative 117 [90]. Cyclization reactions have also been developed as demonstrated in Eqs. (36) and (37) [91 -93]. The main interest of this approach is the high level of functionalization of the final products. 

Scheme 9.19. Reactivity of cyclobutylmethyl and cyclopropylmethyl carbanions [55, 79] and radicals [80].

What, then, about the cyclobutylcarbinyl radical Eq. 3.108 shows the treatment of tricyclic cyclobutylmethyl iodide (268) with Bu3SnH in the presence of AIBN in refluxing benzene solution to generate bicyclic exo-methylene compound (269), via 13-cleavage of the cyclobutylcarbinyl radical. This bicyclic exo-methylene (269) is the skeleton of a terpenoide natural product, guaiane alismol [277-280]. 

Rearrangement of the adducts of crotylmagnesium chloride to styrene [Eq. (14)] was also reported (46). The cyclization appears to follow an unusual course in producing the larger of two possible rings. In previously reported organometallic (29) or radical (43) cyclizations, the smaller-ring cycloalkylmethyl skeleton is the kinetically determined product (i.e., cyclobutylmethyl rather than cyclopentyl, or cyclopentyl-methyl rather than cyclohexyl). 

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