Reactivity and Diastereoselectivity in the Thermal and Lewis Acid-Catalyzed Diels−Alder Reactions of N-Sulfinylphosphoramidates1
摘要:
The [4 + 2] cycloaddition reactions of N-sulfinvlphosphoramidates, prepared from the corresponding phosphoramidates by treatment with N-(chlorosulfinyl)imidazole, and 1,3-cyclohexadiene were found to be diastereoselective in the absence (>90:10)and presence (>95:5) of Lewis acid. The sulfur configuration of the major adduct from the cycloaddition reaction has been established unambiguously by X-ray crystallography. The use of Lewis acids improved the diastereoselectivity and yield, as well as shortened reaction times. Based on the intermediacy of a tin chelate, and the absence of phosphoryl secondary orbital interactions, a mechanism for the cycloaddition reactions is discussed.
Stereoselective Synthesis of Nipecotic Acid Derivatives via Palladium-Catalyzed Decarboxylative Cyclization of γ-Methylidene-δ-valerolactones with Imines
作者:Ryo Shintani、Masataka Murakami、Tamio Hayashi
DOI:10.1021/ol802569q
日期:2009.1.15
A new synthetic method of multisubstituted nipecotic acid (piperidine-3-carboxylic acid) derivatives has been developed by way of palladium-catalyzeddecarboxylative cyclization of γ-methylidene-δ-valerolactones with imines. By employing the diethoxyphosphinoyl group as the N-protecting group for imines, the reaction proceeds smoothly with high diastereoselectivity. The products thus obtained can be
O,O′-Dialkyl N,N-dibromophosphoroamidates, a novel pseudohalogen-type reagent has been prepared by direct bromination of O,O′-dialkyl phosphoroamidates in aqueous potassium carbonate. The preparative usefulness of these compounds in the synthesis of N-phosphorylated 2-phenylaziridines has been demonstrated.
Diethyl N,N-dichlorophosphoroamidate (DCPA), a stable, easily distillable, but very reactive pseudo-halogen containing phosphorus has been prepared in excellent yield by direct chlorination of diethyl phosphoroamidate in buffered aqueous acid solution. The reaction was found to be of general use for the preparation of some structural analogues of DCPA.