Nickel-Catalyzed Highly Regio- and Stereoselective Cyclization of Oxanorbornenes with Alkyl Propiolates: A Novel Method for the Synthesis of Benzocoumarin Derivatives

Abstract

Transition metal catalyzed cyclizations of alkenes and alkynes are powerful methods for the synthesis of various carbocyclic and heterocyclic compounds. [1] Recently, we [2,3] and others [4,5] observed that nickel complexes effectively catalyze the cycloaddition of 7-oxa-and 7-azabenzonorbornadienes with alkynes to give [22] [2] and [222] [3a,b] cycloadducts (Scheme 1). The reactions of alkenes with Scheme 1. Ni-catalyzed [22] and [222] cycloaddition of 7-oxabenzonorbornadienes with alkynes.

New Catalytic Reactions of Oxa- and Azabicyclic Alkenes

“…Oxabicyclic alkenes undergo cyclization with alkyl propiolates at 80 °C catalyzed by bidentate phosphine nickel complexes to give benzocoumarin derivatives in high yields. For example, treatment of 7-oxabenzonorbornadiene ( 2b ) with methyl butyn-2-oate ( 69a ) in the presence of NiBr 2 (dppe) and zinc metal powder in acetonitrile at 80 °C gave a benzocoumarin product 70a in 87% yield (Scheme ) . Other bidentate phosphines, dppf, dppm, and dppp, are less effective, and monodentate phosphine either exhibited no activity or gave different products (see Schemes 15 and 18).…”

“…For example, treatment of 7-oxabenzonorbornadiene (2b) with methyl butyn-2-oate (69a) in the presence of NiBr 2 (dppe) and zinc metal powder in acetonitrile at 80 °C gave a benzocoumarin product 70a in 87% yield (Scheme 20). 34 Other bidentate phosphines, dppf, dppm, and dppp, are less effective, and monodentate phosphine either exhibited no activity or gave different products (see Schemes 15 and 18). The choice of solvent is also vital to the catalytic reaction.…”

Atom-economical synthesis of 1,2-bis(phosphine oxide)ethanes from calcium carbide with straightforward access to deuterium- and13C-labeled bidentate phosphorus ligands and metal complexes

“…Phosphine ligands play crucial roles in catalysis and organic chemistry. [46][47][48][49][50][51] DPPEO 2 and DPPE are commonly used singly in many catalytic transformations [52][53][54][55][56][57] or as Ni and Co complexes in cycloaddition reactions, [58][59][60][61][62][63][64] C-C bond formations [65][66][67] and polymerizations. 68 Moreover, DPPE complexes with gold and platinum show antitumor [69][70][71] and anticancer 72 activities.…”