Carbopalladation formate anions

The same palladium-catalyzed domino cyclization-anion capture sequence involving carbopalladation of allene (69), which was employed by Grigg et al. for the synthesis of diene 70 (Scheme 10) can yield 1,3,5-hexatriene 194, when starting from 2-bromo-l-ene-6-yne 193 instead of the aryl iodide 68 (Scheme 32) [52], Under the conditions of its formation, 194 immediately undergoes thermal 67r-electrocyclization to give the bicyclic product 195. 

Balme has reported a one-pot threecomponent alkene carboamination between propargylic amines, alkylidene malonates, and aryl halides [43]. For example, treatment of N-methyl propargylamine (2 equiv), dimethyl benzylidene malonate (2 equiv) and 1,4-diiodobenzene (1 equiv) with n-BuLi and a palladium catalyst provided 43 as a single diastereomer (Eq. (1.20)) [43a]. The formation of the C—N bond in this process does not appear to be metal catalyzed. Instead, initial conjugate addition of the nitrogen nucleophile to the activated alkene affords a malonate anion, which undergoes carbopalladation followed by reductive elimination to afford the pyrrolidine product. 

Amines and Alkenes as Factors Affecting the Rates of Both the Oxidative Addition and Carbopalladation The base (NEt ) plays a multiple role. It stabilizes Pd (PPh3)2(OAc) versus its decomposition to Pd"(PPh3)2 by protons and consequently slows down the oxidative addition (Scheme 19.7) [7c, 1, p]. The base accelerates the overall carbopalladation by shifting the equilibrium toward PhPd(OAc)L2 upon quenching the proton (Scheme 19.9) [71]. It favors the recycling of the Pd complex from the hydrido-Pd . The formation of HPd PPhj) was proposed by Heck (Scheme 19.2). In DMF, the cationic [HPd(PPh3)2S] must be formed with acetate as the counter anion (Amatore/Jutand [7m]). 

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