Highly regio- and chemoselective palladium-catalyzed propargylallylation of activated olefins: A novel route to 1,7-enyne derivatives

An efficient method for the synthesis of 1,7-enyne derivatives via phosphine-palladium-catalyzed three-component assembling of activated olefins, allylic chlorides, and allenylstannanes is described. Substituted arylethylidene malononitriles 1a-g (RCH=C(CN)(2): R = C6H5 (1a), p-ClC6H4 (1b), p-OMeC6H4 (1c), p-NO2C6H4 (1d), 1-naphthyl (1e), 2-furyl (1f), and 2-thienyl (1g)) undergo propargylallylation with allylic chlorides 2a-e (allyl chloride (2a), methallyl chloride (2b), 4-chloropent-2-ene (2c), cinnamyl chloride (2d), and 3-chlorocyclohexene (2e)) and n-tributylallenylstannane (n-Bu3SnCH=C=CH2, 3a) in the presence of Pd(PPh3)4 in toluene to afford the corresponding 1,7-enyne derivatives 4a-m in good to excellent yields. The catalytic reaction is highly regioselective, with the propargyl group adding to the carbon where the R group is attached and the allyl group adding to the carbon connected to the CN groups of activated olefins la-g. The present catalytic reaction is successfully extended to substituted arylethylidene-1,3-indanediones 5a-j (RCH = (1,3-indanedione): R = C6H5 (5a), p-ClC6H4 (5b), p-BrC6H4 (5c), p-OMeC6H4 (5d), p-NO2C6H4 (5e), p-CNC6H4 (5f), p-biphenyl (5g), 1-naphthyl (5h), 2-thienyl (5i), and 2-benzo[b]furane-2-yl (5j)) and substituted 2,2-dimethyl-5-(arylethylidene)-1,3-dioxane-4,6-diones 7a,b (RCH = (1,3-dioxane-4,6-dione): R =p-NO2C6H4 (7a),p-OMeC6H4 (7b)). The three-component assembling of these substrates with allylic chlorides (2a,b,d,e) and n-tributylallenylstannane (n-Bu3SnCH=C=CH2, 3a) proceeds smoothly to afford the corresponding 1,7-enyne derivatives 6a-m and 8a-d in good to excellent yields. The catalytic propargylallylation can be further applied to the activated dienes, C6H5CH=CH=CR2 (R-2 = (CN)(2) (9a), 1,3-indanedione (9b), 2,2-dimethyl-1,3-dioxane-4,6-dione (9c)), with allylic chlorides (2a,b,d) and allenylstannane 3a to give regio- and chemoselective 1,2-addition products 10a-h in good to excellent yields. A plausible mechanism based on an eta(1)-allenyl eta(3)-allyl palladium intermediate is proposed to account for the catalytic three-component reaction.