Methyl nitrile ylide was generated by both a photochemical and desilylation route and has been characterized by UV spectroscopy and by its kinetic and cycloaddition behavior. The dipole is formed by the addition of singlet methylene to acetonitrile and shows a strong transient absorption at 280 nm which is quenched by the addition of standard dipolarophiles. The relative rates of formation of 1,3-dipolar adducts and the relative rates of quenching of the transient absorption are in excellent agreement. Generation of the dipole from a silylthioimidate followed by dipolar cycloaddition also gave rise to related cycloadducts. The ratio of cycloadducts obtained from an unsymmetrically substituted dipolarophile was found to be strikingly dependent on the purity of the silylthioimidate. The different product ratios result from the operation of an alternate mechanism which involves the thiophenol that is released in the decomposition of silylthioimidate to the nitrile ylide. The initially generated dipole is believed to react with excess thiophenol to give a “half-capped” dipole which undergoes a subsequent conjugate addition to the unsymmetrical dipolarophile.
ASJC Scopus subject areas
- Colloid and Surface Chemistry