Among the various classes of sesquiterpene a-methylene-y-butyrolactones, the pseudoguaianolides' are unparalleled as structural and stereochemical challenges2 to the discriminating synthetic organic chemist. I II III We herein report an extremely facile pseudoguaiane construction of potential value for total synthesis of 8,12-olides. The present sequence culminates with damsinic acid(III), a congener (and possible biosynthetic precursor) of damsin, which possesses the same relative configuration of I, II and other pseudoguaianolides at carbons 1,5,7 and 10, as well as most of their functionality. Key elements of our synthesis are: 1) intramolecular carbonium ion attack on a terminal alkyne group6 to generate hydroazulenedione 2 in only three steps; 2) protection of the lesshindered 7-carbonyl group while introducing the desired chirality at carbons 1, 5 and 10, (3 + fj), and 3) introduction of carbons 11-13 by initial nucleophilic attack at C7 = 0 (d-+ L), instead of more typical electrophilic alkylation of endocyclic enolates 394 . Propargylation of 2-methyl-1,3-cyclopentanedione in aqueous sodium bicarbonate affords 1 _7, mp 71.5-72', in 85% yield. Treatment of 1 with two equivalents of 2-lithiopropene (prepared by lithiumhalogen exchange of 2-bromopropene with t-butyllithium8 gives carbinol 2. (separable epimers); heating (80"/1 hr) in 90% formic acid affords oily diketone J7 (vfilm 1740, 1700 cm-') in ~50% yield. Diketone 3 reacted preferentially at the cycloheptanoid carbonyl group with a No