Stereoselective [2 + 2 + 2] cocyclotrimerization of oxa- and azabenzonorbornadienes † with alkynes catalyzed by nickel complexes: first transition metal-mediated synthesis of isobenzofuran and isoindole precursors

Abstract

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

“…Transition metal catalyzed cyclizations of alkenes and alkynes are powerful methods for the synthesis of various carbocyclic and heterocyclic compounds 1. Recently, we2, 3 and others4, 5 observed that nickel complexes effectively catalyze the cycloaddition of 7‐oxa‐ and 7‐azabenzonorbornadienes with alkynes to give [2+2]2 and [2+2+2]3a,3b cycloadducts (Scheme ). The reactions of alkenes with alkynes depend greatly on the reaction conditions.…”

“…Other bidentate phosphines such as 1,1′‐bis(diphenylphosphanyl)ferrocene (dppf), methylenebis(diphenylphosphane) (dppm), and 1,3‐propanediylbis(diphenylphosphane) (dppp) are less effective, giving 3 a in 53, 47, and 26 % yield, respectively. Nickel complexes of monodentate phosphines that are efficient catalysts for the [2+2]2 and [2+2+2]3a,3b cycloaddition of 1 a with various alkynes are essentially inactive in the formation of 3 a .…”

Transition Metal Catalyzed [2+2+2] Cycloaddition and Application in Organic Synthesis

“…The same catalyst has also been found to be effective for the cycloaddition of 1,2‐bis(propiolyl)benzene to provide anthraquinone derivatives at room temperature 52b. McDonald and co‐workers have utilized intramolecular cyclotrimerization of diyne and C ‐alkynylglycosides for the synthesis of anthraquinone C ‐glycosides,52c whilst Cheng and co‐workers have studied a series of nickel‐catalyzed [2+2+2] cyclizations of oxa‐ and azabenzonorbornadienes with terminal alkynes and bis‐alkynes for construction of multi‐fused ring systems 53. It was noted that temperature control was necessary for the successful isolation of cyclotrimerized products.…”

Versatile Catalytic Reactions of Norbornadiene Derivatives with Alkynes

“…A detailed study of this nickel‐catalyzed [2+2+2] cyclotrimerization reaction was done by the same group . The reaction of oxabenzonorbornadiene with various alkynes resulted in two common products 85a and 85b regardless of the alkyne used [Eq.…”