エナミンを経由するキラルなアルデヒド系香気物質の光学活性化

抄録

Some aldehydes are widely used as an artificial perfume. However, little has been known on the optically active aldehydes. In order to obtaine the optically active aldehydes, enamines were synthesized from racemic aldehydes and optically active amines which were derived from natural amino acids. The optically active aldehydes were recovered from the hydrolysis of the enamines under various conditions. The aldehydes employed were 3-p-cumenyl-2-methylpropionaldehyde (CPA) and 2-methyl-3-phenylpropionaldehyde (MPA), which had similar structure to CPA. CPA is employed as an artificial perfume (Cyclamenaldehyde). The acids employed for the hydrolysis were hydrochloric acid or cation exchange resin.
When the amine components of the enamines were (S) -3-isopropylmorpholine (1a) and (S) -3-isobutylmorpholine (1b), (+) -aldehyde was recovered. However, in the case where (S) -3-benzylmorpholine (5) was employed, (-) -aldehyde was recovered.
In order to evaluate the optical purity of recovered aldehydes, the aldehydes were converted to corresponding alcohols, the optical rotation of which were compared with those values for the optically pure alcohol synthesized from the corresponding optically pure acid. The specific rotations of the optically pure MPA and CPA were determined as follows ;
[(S) -MPA [α] ²⁵₄₃₅=+9.10° (c=6.21 in benzene)]
[(S) -CPA [α] ²⁵₄₃₅=+13.9° (c=6.87 in benzene)]
The odor of (+) -CPA was compared with that of (-) -CPA, and there was clear difference between the odors of (+) -and (-) -CPA.