Jeffery’s ligandless conditions

T. Jeffery, Tetrahedron Lett., 1985, 26, 2667 J. Chem. Soc., Chem. Common., 1984, 1287 and R. Larock and B. E. Baker, Tetrahedron Lett., 1988, 29, 905. These reaction parameters are sometimes referred to as Jeffery s ligandless conditions. ... 

Cyclization of the quinoxaline chloride 50 to prepare pyrrolo[2,3-f ]quinoxaline under usual conditions is slow and the yield is low, because the aminoquinoxa-lines are strong chelating agents and poison Pd catalysts. However, the locked Pd catalyst is released and the reaction proceeds smoothly under Jeffery s ligandless conditions to give the pyrrolo[2,3- ]quinoxaline 51 in 67 % yield [38]. 

Interestingly, HR of < -bromobenzaldehyde (93) with acrylate gave the doubly substituted product 94 and the expected product 95 under Jeffery s ligandless conditions [60]. Eormation of 94 is explained by the following mechanism. Insertion of acrylate to 93, followed by oxidative addition of aldehyde generates 96. The palladacycle 97 is formed by decarbonylation, and its reductive elimination gives 98. The final product 94 is obtained by HR of 98 with acrylate. 

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