Synthesis of the cytotoxic isoquinoline quinone perfragilin A, an improved synthesis of perfragilin B and preparation of some analogues of both these compounds are described. Cytotoxicity evaluation of a number of the products is reported. The regioselectivity in Diels– Alder reactions of differently substituted benzoquinones with 2-aza-1, 3-bis (t- butyldimethylsilyloxy)-1, 3-butadiene is described.