A Mitsunobu-Michael Reaction Sequence to N-Heterocyclic Variants and Ti(III)-Mediated Synthesis of Terpenoids and N-Fused Indoles

Abstract

The research work delineates a flexible and novel route for the diastereoselective construction of diversely substituted N-heterocyclic variants as valuable scaffolds for natural products and pharmaceuticals, starting from an easily accessible prochiral α-phenyl-β-enamino ester. By taking advantage of the Cp2TiCl-mediated reductive epoxide opening-cyclization, an expedient and unified approach has been accomplished to gain access to a handful of iridoid monoterpenes in an enantiomerically divergent manner starting from (+)-β-citronellene. Also, a radical approach to build oxa-quaternary centers, structural feature of various natural-products-inspired synthons have been undertaken via Cp2TiCl-mediated reductive epoxide opening-cyclization protocol. Furthermore, the feasibility of Cp2TiCl-promoted radical cyclization has also been explored onto N-tethered epoxy indoles which provide an efficient route for the construction of pyrrolo/piperidino[1,2-a]indole derivatives.