Regio- and stereoselective reductive coupling of bicyclic alkenes with propiolates catalyzed by nickel complexes: A novel route to functionalized 1,2-dihydroarenes and γ-lactones

[[abstract]]7-Oxabenzonorbornadienes derivatives 1a-d underwent reductive coupling with alkyl propiolates CH3C equivalent CCO2CH3 (2a), PhC equivalent CCO2Et (2b), CH3(CH2)3C equivalent CCO 2CH3 (2c), CH3(CH2)4C equivalent CCO 2CH3 (2d), TMSC equivalent CCO2Et (2e), (CH3)3C equivalent CCO2CH3 (2f) and HC equivalent CCO2Et (2g) in the presence of [NiBr2(dppe)] (dppe=Ph2PCH2-CH2PPh2), H2O and zinc powder in acetonitrile at room temperature to afford the corresponding 2-alkenyl-1,2-dihydronapthalen-1-ol derivatives 3a - n with remarkable regio- and diastereoselectivity in good to excellent yields. Similarly, the reaction of 7-azabenzonorbornadienes derivative 1e with propiolates 2a, b and d proceeded smoothly to afford reductive coupling products 2-alkenyl-1,2-dihydronapthalene carbamates 3o-p in good yields with high regio- and stereoselectivity. This nickel-catalyzed reductive coupling can be further extended to the reaction of 7-oxabenzonorbornene derivatives. Thus, 5,6-di(methoxymethyl)-7-oxabicyclo[2.2.1]hept-2-ene (4) reacted with 2a and 2d to furnish cyclohexenol derivatives bearing four cis substituents 5a and b in 81 and 84 % yield, respectively. In contrast to the results of 4 with 2, the reaction of dimethyl 7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboxylate (6) with propiolates 2a-d afforded the corresponding reductive coupling/cyclization products, bicyclo[3.2.1]γ-lactones 7a-d in good yields. The reaction provides a convenient one-pot synthesis of γ-lactones with remarkably high regio- and stereoselectivity.[[fileno]]2010326010007[[department]]化學