Synthesis and odour evaluation of stereoisomers of octahydrobenzopyran derivatives

The synthesis and isolation of the four racemic 2,5,5,8a‐tetramethyl‐3,4,4a,5,6,7,8,8a‐octahydro‐2 H ‐1‐benzopyran stereoisomers from β ‐ionone and α ‐ionone is reported. It was based on the cyclization of dihydro‐ β ‐ionone and dihydro‐ α ‐ionone with chlorosulfonic acid at low temperature to yield stereospecifically the trans ‐fused and cis ‐fused hexahydrobenzopyran derivatives, respectively. The direct cyclization of dihydro‐ β ‐ionol and dihydro‐ α ‐ionol under identical conditions was also explored. In addition to the complete spectroscopic characterization of every isolated isomer, a description of their olfactory properties is displayed. Copyright © 2006 John Wiley & Sons, Ltd.