Journal of the American Chemical Society, Vol.119, No.21, 4911-4920, 1997
Nickel-Catalyzed Organozinc-Promoted Carbocyclizations of Electron-Deficient Alkenes with Tethered Unsaturation
A nickel-catalyzed method for cyclizations of electron-deficient alkenes with tethered unsaturation in the presence of organozincs was developed. Considerable flexibility in the structure of each reactive component was observed. Enones, alkylidene malonates, unsaturated beta-ketoesters, and nitroalkenes participated as the electron-deficient alkene; alkynes, enones, 1,3-dienes, and aldehydes participated as the tethered unsaturation; and a variety of sp(2) and sp(3)-hybridized organozincs, including those that possess beta-hydrogens, participated as the nucleophilic component. Substrate structure, organozinc structure, and ligand structure all played a significant role in determining product selectivities. Of particular synthetic significance was the opportunity to prepare either E or Z tri- or tetrasubstituted alkenes from a common alkyne. A discussion of probable mechanisms is provided.
Keywords:O-STANNYL KETYLS;(+/-)-SCOPADULCIC ACID-A;ORGANIC-SYNTHESIS;CONJUGATE ADDITION;REAGENTS;CYCLIZATIONS;ALDEHYDES;COMPLEXES;KETONES;NICKELOCYCLOPENTANES