Preparation of Carbocyclic and Heterocyclic Compounds by the Use of an Allylzinc and an Allylpalladium in Tandem

During the last decade, part of our work was directed at the construction of methylene derivatives of five- and six-membered carbocyclic and heterocyclic compounds (1): methylenecyclopentenes, methylenecyclopentanes, methylenetetrahydrofurans, methylenepyrrolidines and methylenetetrahydropyrans. Our routes start with the addition of 2-(metallomethyl)-2-alkenyl ethers (2) to C≡C, C=X (X = C, O, NR), and epoxides (3) to give 4, which can be derivatized or, more importantly, cyclized to 1 in situ by Pd(0) catalyzed elimination of met-OR². Special features are the one-pot nature, cleanliness and mildness of most procedures leading to 1. So far, we have found that silyl ether, acetal and ester groups as well as primary C-Cl remain unaffected by zinc reagents 2 (met=ZnBr) under our reaction conditions.¹ In initial studies, 3-metallomethyl derivatives of 5-methylenetetrahydropyrans and 5-methylene-N-methylpiperidine were obtained by an intramolecular version of the addition step, a type-II zinc-ene reaction of 2-(bromozincmethyl)-2-propenyl alkenyl ethers and N-methyl-N-{2-(chloromagnesiomethyl)-2-propenyl}allylamine, respectively. An extension of the main theme concerns the preparation of 3,4-dimethylene derivatives of tetrahydropyran and N-methylpiperidine.

Cyclopentenes - cyclopentanes - tetrahydrofurans - pyrrolidines - tetrahydropyrans