Rearrangement of the Grignard reagent from 1-methylcyclobutylmethyl bromide: origins of the methyl substituent effect

Article abstract of DOI:10.1016/0022-328X(88)83115-2

1-Methyl substitution leads to a small decrease (ca. 0.45) in the rate of the ring cleavage rearrangement of cyclobutylmethylmagnesium bromide.Comparison with literature data for 3- and 5-membered rings indicates that the methyl substituent shifts the equilibrium in the direction of ring cleavage, mostly by stabilization of the double bond of the open isomer, and possibly partly by destabilization of the organometallic function of the cyclic isomer.The reaction rate is decreased in both directions, probably because of increased transition state steric repulsions.