A New α,β‐Enone → Alkynone Fragmentation. Syntheses of exaltone® and (±)‐muscone

p ‐Toluenesulfonylhydrazones of α, β‐unsaturated ketones undergo an alkynone fragmentation in high yield when treated with electrophiles under basic conditions. With N ‐bromosuccinimide in alcohols, the p ‐tosylhydrazones 4a and 4b yielded in a one‐pot reaction the cyclic 4‐alkyn‐1‐ones 5a and 5b ; these were converted to Exaltone® ( 1a ) and muscone ( 1b ) on catalytic hydrogenation.