High-yielding preparation of fragrance Clarycet via two-step synthesis

Clarycet (4-methyl-2-propyltetrahydro-2H-pyran-4-yl acetate) is an important fragrance used in many industrial applications ranging from cosmetics to agrochemical products. There are several procedures for its preparation, while two-step synthesis consisting of Prins cyclization followed by esterification appears to be simpler and higher yielding comparing to other procedures. Therefore, we sought for the optimal reaction conditions of both steps. We found that the highest yields of the desired substituted tetrahydropyranol (THPol) in Prins cyclization of butanal with isoprenol can be achieved under the following conditions: 70 degrees C, catalyst 1 mol% 10% sulphuric acid, 250 mol% of water, no solvent (butanal conversion 93%, selectivity to THPol 82% after 5 h of reaction). The second reaction step, esterification of THPol with acetic anhydride, was optimized yielding 98% of Clarycet under the following reaction conditions: molar ratio THPol:acetic anhydride 1:5, catalyst 1 mol% FeCl3, room temperature, no solvent, 5 min of reaction. The availability of the catalysts used, the possibility of performing the reactions without the addition of the solvent, and the high yields of the product showed good potential of this arrangement for Clarycet preparation.