Addition of iodine etectrophiles to buta-1,3-diene: effects of charge distribution and ion-pair stability on product ratios

Abstract

The addition of the following iodine electrophiles to buta-1,3-diene is described: tert-butyl hypoiodite (Bu^tOl) in the presence of BF₃, acetyl hypoiodite (AcOl), iodine monochloride (ICl) and iodine monobromide (IBr). Data from tert-butyl hypobromite (Bu^tOBr) and tert-butyl hypochlorite (Bu^tOCl) with buta-1,3-diene and BF₃ are reported for comparison. All of the electrophiles give mixtures of M 1,2- and 1,4-addition, but no AM 1,2-products. Radical reactions are reported for Bu^tOl, Bu^tOBr and Bu^tOCl. Greater 1,4-addition occurs for the electrophiles with anions of lower basicity (IBr and ICl), and the halonium ion with increased dispersal of charge (Bu^tOCl). The results are rationalized from the viewpoints of charge density and ion-pair stability.