Identification of a precursor to naturally occurring β-damascenone

9-Hydroxymegastigma-3,5-dien-7-yne 8a was synthesised and shown to be identical to an intermediate found in the acid-catalysed conversion of 3,5,9-trihydroxymegastigma-6,7-diene 4 to beta -damascenone 1, 3-hydroxydamascone 5 and megastigma-5-en-7-yne-3,9-diol 6. When subjected to acid hydrolysis, 8a produced beta -damascenone 1, in high yield. Importantly, the hydrolysate was completely free of 3-hydroxydamascone 5. (C) 2001 Elsevier Science Ltd. All rights reserved.