Anwendung von Ringerweiterungen zur Herstellung von <i>rac</i>‐Muscon und Exalton^®

Abstract

Application of Ring Expansions for the Preparation of rac ‐Muscone and Exaltone ® 4,6‐Undecamethylene‐2‐pyrone (8), prepared from 1‐morpholino‐cyclododec‐1‐ene (7) according to Hünig et al. , was saponified and decarboxylated to a mixture of the 3‐methyl‐cyclotetradecenones 11, 12, 13 and 14, which was hydrogenated to 3‐methyl‐cyclotetradecanone (3). Similarly, 4,6‐dodecamethylene‐2‐pyrone (16) was prepared from 1‐morpholino‐cyclotridec‐1‐ene (15) and ketene, saponified to a mixture of the 3‐methyl‐cyclopentadecenones 19, 20, 21 and 22 and the latter hydrogenated to rac‐muscone (6). The ratios of the four regio‐ and stereoisomers in the above mentioned two mixtures of 3‐methyl‐cycloalkenones were derived from the 1 H‐NMR.‐spectra. From the reactions of the enamines 7 and 15 were also isolated small amounts of 4,5‐decamethylene‐ (9) and 4,5‐undecamethylene‐6‐methyl‐2‐pyrone (17) respectively. Saponification and partial decarboxylation of 9 lead to (2‐acetyl‐cyclododec‐1‐enyl)‐acetic acid (23) and methyl‐(2‐methyl‐cyclododec‐1‐enyl)‐ketone (24), the latter possessing an incense‐like odor. The keton homologation method of Mock &amp; Hartman (reaction of alkanones with diazoacetic ester in the presence of triethyl oxonium fluoroborate, followed by saponification and decarboxylation) was applied three times in succession, starting with cyclododecanone (1). This furnished, after the first stage, the cyclotridecanone (4) required for the above described synthesis of rac ‐muscone (6) and, after the third stage, cyclopentadecanone (5 = exaltone ® ). Application of this reaction to 2‐methyl‐cyclododecanone (28) resulted in a low yield of 2‐methyl‐ (30) and 3‐methyl‐cyclotridecanone (31) in the ratio of 2:1.