Geranyl diethyl amine

Prins reaction of P-pinene with formaldehyde gives the alcohol nopol (39) and its acetate [35836-72-7] (40) is used as a fragrance ingredient. Base-catalyzed addition of dieth-ylamine to myrcene gives geranyl diethyl amine (41), which is converted to menthol (42) as described below. 

The synthesis starts with myrcene (32), which can be obtained from 3-pinene as described above. Addition of the diethylamide anion gives geranyl diethyl amine (41). Isomerization using ruthenium (S)-BINAP gives the A,A-diethylenamine of enantiomeric excess (ee) of >96% and the catalyst turn over number is 400,000, which makes the process very efficient. The remainder of the synthesis follows that of the standard synthesis of /-menthol from citronellal. The zinc-catalyzed ene reaction converts /-citronellal to /-isopulegol [89-79-2] (172) and this is hydrogenated to /-menthol (42). More detail on this chemistry is given below. 

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