Chapter 8 - Applications of the Sonogashira reaction in the total synthesis of alkaloids

Abstract

The Sonogashira cross-coupling reaction is an important and useful name reaction in organic synthesis in which carbon–carbon bonds are generated. It uses a Pd species as a catalyst and copper as a cocatalyst to form a carbon–carbon bond between a terminal alkyne and an aryl or vinyl halide. The Pd-catalyzed C–C bond formation process, which can couple a terminal sp hybridized carbon from an alkyne with an sp2 carbon of an aryl or sp2 vinyl halide (or triflate), is generally known as a Sonogashira cross-coupling reaction. The reaction arose in 1975 from the development of a C–C bond formation by a Pd species such as PdCl2(PPh3)2 as catalyst combined with a cocatalytic amount of CuI and an amine at ambient temperature by a research group led by Kenkichi Sonogashira. Notably, this discovery was introduced several months after Cassar and Dieck and Heck discovered that it was possible to perform this coupling not only under Pd catalysis but also by proceeding at high temperature. Sonogashira's conception was to combine Cu-mediated transmetalation of alkynes, which was known, with a more adaptable, influential, and prevailing metal in catalytic terms, such as palladium, thus providing an extension of Cassar and Heck's results that yielded a strong C–C bond-formation procedure. The ‘‘Sonogashira coupling reaction’’ is currently a comprehensive depiction applied to the Pd(0)-catalyzed coupling of a sp2 (or even sp3) halide or triflate with a terminal alkyne (sp), irrespective of whether copper(I) salts are used or not. In this chapter, we try to follow and cover, the total synthesis of alkaloids using Sonogashira coupling reaction.