Abstract:
C−h activation by transition metals has revolutionized the field of modern synthetic organic chemistry thereby enabling efficient and atom-economical construction of complex organic frameworks in reduced number of steps. Various ways are being explored in order to maximize efficiency of the approach and construct previously unknown molecules. The major challenge in this aspect is the ubiquitous presence of c−h bond in an organic molecule that demands sophistication to achieve site-selective functionalization. Directing group approach provided the most viable solution which operates through formation of a thermodynamically preferred metallacycle. Although, five and six membered metallacycles are known to be thermodynamically most favorable, there exists ingenious methodologies that operates through a four-membered metallacycle in order to achieve site-selectivity. In this review article, we summarize the c−h activation reactions evidenced to proceed via four-membered metallacycle intermediate to achieve synthetically relevant transformations. © 2021 wiley-vhca ag, zurich, switzerland