Oxiranylmethyl‐Fragmentierung zur Bildung von Cyclopentadecan‐1,5‐dion‐Derivaten. Eine Musconsynthese

The Formation of Cyclopentadecane‐1,5‐dione Derivatives by an Oxiranylmethyl Fragmentation. A Synthesis of Muscone A new method for the preparation of cyclopentadecane‐1,5‐dione ( 11 ) and its 3‐methylderivative 12 , compounds with a musk fragrance, is described. Starting from the readily available bicyclic enones 9 and 10 , the epoxy‐ p ‐toluenesulfonate 15 and its methylderivatives 20A and 20B were prepared by reduction with diisobutyl‐aluminium hydride or sodium borohydride (to 13 and 18A , 18B ), epoxidation with m ‐chloroperbenzoic acid (to 14 and 19A , 19B ), followed by tosylation. Heating of 15 and 20A or 20B with calcium carbonate in water/dioxane under reflux caused fragmentation leading to the diketones 11 and 12 in high yields. The same fragmentation also occurred with sodium hydrogencarbonate in dimethylsulfoxide at 160°, but in lower yields. The conversion of 12 into rac ‐muscone ( 2 ) was accomplished by developing a method for selectively forming the monotosylhydrazone 27 . The latter was reduced with sodium borohydride and the crude alcohol 28 oxidized to 2 . Unexpectedly the pyrolysis of the epoxy‐acetate 29 at 350° in a sealed glass tube led to the bicyclic ketone 10 . Treatment of 3‐methylcyclopentadecane‐1,5‐dione ( 12 ) with peracetic acid and boron trifluoride etherate gave the stable crystalline ozonide 33 .