Reactions of Cyclopropylcarbinyl Halides with (Trimethylstannyl)alkalis.Evidence That Kinetically Free Intermediates Need Not Be Involved in Cyclopropylcarbinyl to 3-Butenyl Rearrangements

Article abstract of DOI:10.1021/jo00181a027

Studies on the reactions of cyclopropylcarbinyl bromide and iodide with trimethylstannyl anionoids have been made with emphasis on counterion, solvent, and addend (tert-butylamine and dicyclohexylphosphine) effects.Both halides yield cyclopropylcarbinyl- and 3-butenyltrimethylstannanes as major products.Depending upon reaction parameters much or all of the latter is shown to be formed by a mechanism or mechanisms which do not involve kinetically free radical or ionic intermediates.With cyclopropylcarbinyl bromide no electron transfer (ET) (free radical) component isobserved in THF or in THF containing 18-crown-6.However, in 20 percent THF- 80 percent benzene a small extent of the ET mechanism is observed in the presence of DCPH.The iodide reacts in THF via S_N2 (or equivalent) and halogen-metal exchange (HME) mechanisms leading to the formation of both methylcyclopropane and 1-butene in the presence of traps, indicating that the cyclopropylcarbinyl anion can undergo rearrangement to the 3-butenyl anion in competition with other processes.In the presence of 18-crown-6 and DCPH a small ET component is observed with the iodide.