Palladium‐Catalyzed Cyclization of Enediynes to Benzopyranones

Abstract

Treatment of methyl 2-[6-substituted-3(Z)-hexen-1,5-diynyl]benzoates (1) with five mol% of palladium chloride and three equivalents of cupric chloride in refluxing acetonitrile gave dibenzoA C H T U N G T R E N N U N G [b,d]pyran-6-ones (2) in modest to good yields.

Synergistic Effect of Palladium and Copper Catalysts: Catalytic Cyclizative Dimerization of ortho‐(1‐Alkynyl)benzamides Leading to Axially Chiral 1,3‐Butadienes

“…However, incorporation of a methyl group at the C3 position of the benzamide 1 inhibited the cyclization completely presumably due to the steric hindrance (Table 2, entry 13). Finally, while o ‐(1‐alkynyl)benzoic ester was inactive towards the cyclization under our conditions,18 the o ‐(1‐alkynyl)benzoic acid 5 underwent the cyclizative dimerization smoothly to furnish the dimer 6 in 52 % yield (Scheme ) 19. The structure of 6 was determined by X‐ray analysis (see the Supporting Information).…”

Nucleophilic cyclizations of enediynes as a method for polynuclear heterocycle synthesis

“…Heating of acetonitrile solutions of 2-[6-R-3-(Z)-hexene-1,5-diynyl]benzoates 36 with palladium(II) and copper(II) chlorides produces dibenzopyranones 37 (Scheme 23) [38]. If the substituent R is bulky a certain amount of cyclopenta[c]isochromenone 38 is formed together with the main product 37.…”

Recent advances in heterobimetallic palladium(ii)/copper(ii) catalyzed domino difunctionalization of carbon–carbon multiple bonds

“…of CuCl 2 gave the tricyclic products 108 (Scheme 46). 57 The proposed sequence involved the nucleophilic attack of the carbonyl oxygen of the ester functionality on the internal alkyne to give the intermediate oxonium ion 109, followed by the 6-endo cyclization and displacement of the methyl group with the assistance of the chloride ion. If a bulky substituent is present at the 6-position of the chain, the 5-exo-dig cyclization compound 110 is also obtained as a minor product.…”