Synthesis of Heterocyclic Molecules Employing Metal Catalysed Atom-economic Couplings and Sustainable Dearomatization Techniques

Abstract

The demand for the synthesis of new chemicals in an environmentally benign fashion is a great challenge to the synthetic chemical community. Development of green technology has emerged as a discipline that permeates all aspects of synthetic chemistry. A major goal of this endeavor must be to maximize the efficient use of raw materials and simultaneously to minimize waste. Thus, synthetic efficiency has to address not only selectivity (i.e. chemo-, regio-, diastereo-, and enenatioselectivity) but also atom economy. With the continuation of the recent trends, we have focused on the development of new strategies for the synthesis of heterocyclic molecules by using ruthenium catalysis, gold catalysis, and photoredox catalysis in an atom-economical fashion. In ruthenium catalysis, the non-metathesis coupling of 5-aminopent-2 yn-1-ol and pent-2-yne-1,5-diol with Michael acceptor in presence of catalytic amount of [CpRu(MeCN)3]PF6 delivered to β-amino and β-hydroxy enones which are readily converted to a series of heterocyclic molecules like 4-piperidone, 4 pyranone, hexahydroisochromenone and isochroman-6-ol. By using gold catalysis, heterocyclic molecules like pyrrole, 5,6-dihydropyridin-3(4H)-one, hydroxy indole, hydroxy benzofuran are synthesized via the activation of propargylic alcohols. In photoredox catalysis, the naurally occuring vitamin molcules like riboflavin tetraacetate are used for dearomative spiro-etherification of naphthols.