The Photobromination of (+)-1-Cyano-2-methylbutane

Abstract

The photobromination of (±)-1-cyano-2-methylbutane with molecular bromine, under varying conditions, yields a mixture of three monobrominated products: 1-cyano-1-bromo-2-methylbutane (relative yield 78–95%), 1-cyano-3-bromo-2-methylbutane (relative yield 1–5%), and 1-cyano-2-bromo-2-methylbutane (relative yield 4–17%). The production of the major monobrominated product is proposed to arise by an acid catalyzed ionic reaction. When the bromination of (+)-1-cyano-2-methylbutane was carried out in the presence of solid N-bromosuccinimide as well as molecular bromine, the three monobrominated products were formed in relative yields that reflected a free radical bromination reaction: (+)-1-cyano-1-bromo-2-methylbutane (5–14%), (±)-1-cyano-2-bromo-2-methylbutane (68–85%), and (+)-1-cyano-3-bromo-2-methylbutane (10–19%).The inability to obtain active 1-cyano-2-bromo-2-methylbutane from these bromination reactions may not be due to the fundamental nature of the bromination of a substrate at a chiral center but may be due to the instability of this particular tertiary bromide.