Effects of Phenyl and Alkyl Substitutions on the Hydrogenation of Allene with Diimide

Article abstract of DOI:10.1021/jo01297a012

Hydrogenation of phenylpropadiene, 3-phenyl-1,2-butadiene, 1-phenyl-1,2-butadiene, and 1-phenyl-1,2-pentadiene with diimide (HN=NH) in refluxing methanol was conducted.The product distribution was analyzed as a function of reaction time, and the selectivities of the addition as well as relative reactivities were determined.Adverse steric effects of the phenyl group at the terminus of one double bond against "cis-coplanar" attack of diimide on the other double bond were found to be remarkably large.Alkyl groups activated the remote double bond of alkylallenes noticeably.This apparent electronic effect was theoretically rationalized from ab initio STO-3G model calculations of the chemical interactions.