Trapping of cyclopentadienone as a 4? component in Diels-Alder reactions with ethyl acrylate: A simple synthesis of (±)-sarkomycin

Heating 4-bromo-2-cyclopentenone in the presence of excess EtO2CCH:CH2 in (MeOCH2)2 in the absence of base for 3 days gave the cyclopentadienone Diels-Alder adduct I. Acetalization of I with 2-methyl-2-ethyl-1,3- dioxolane followed by oxidn. and Jones reductive quenching with NaBH4 gave 70% lactone II. Jones oxidn. of II gave cyclosarkomycin (III), a known precursor of sarkomycin, in 38% overall yield.