Intramolecular Diels-Alder Reaction of α,β-Unsaturated Ester Dienophiles with Cyclopentadiene and the Dependence on Tether Length

Article abstract of DOI:10.1021/jo00263a034

Cyclopentadiene compounds, tethered to an α,β-unsaturated ester functionality, have been prepared by the direct alkylation of the corresponding iodide or tosylate with cyclopentadienylmagnesium chloride.For exemple, tso-CH2CH2C(CH3)2CH=CHCO2C(CH3)3 reacted with cyclopentadienylmagnesium chloride at 0 deg C to yield the alkylated cyclopentadiene, which on heating at 75 deg C underwent a Diels-Alder reaction to give an 81percent yield of 4,4-dimethyltricyclo<5.2.1.0^1,5>dec-8-ene-6-carboxylic acid, tert-butyl ester.Isomerization of cyclopentadiene isomers, common with lithium and sodium carbanions, is not displayed with the Grignard reagent.Several functionalized cyclopentadienes have been prepared which differ in tether length.These substrates readily undergo intramolecular <4+2> cycloaddition at mild temperatures to produce tricyclic ring systems.The cycloaddition will proceed at even lower temperatures if catalyzed by diethylaluminum chloride.Pathways of cycloaddition favor incorporation of the tether linkage into a five- or six-membered ring.