Simple syntheses of dihydrojasmone and cis-jasmone via 1,4-diketones

Two new routes for the synthesis of dihydrojasmone (10a) and cis-jasmone (10b)via 1,4-diketones (5a and b) are described. For the first route, pent-4-en-1-ol (1) was oxidised to the corresponding aldehyde (2), which on reaction with suitable Grignard reagents gave the olefinic alcohols (3a and b). The former (3a) was oxidised directly to the diketone (5a) by Jones reagent catalysed by Hg-(OAc)2. The latter (3b) was oxidised stepwise, first by PCC to give (4), then by PdCl2 to yield (5b). For the second route, pent-4-yn-1-ol (6) was converted to the aldehyde (7), which on Grignard reaction using suitable reagents gave the hydroxy-acetylenes (8a and b). These were oxidised to the corresponding acetylenic ketones (9a and b), which in turn were converted by Hg2+ catalysed hydration to (5a and b). Base cyclisation of the diketones (5a and b) yielded (10a and b) respectively.