Synthesis of (<i>R</i>)‐ and (<i>R</i>)‐4‐methyl‐6‐2′‐methylprop‐1′‐enyl‐5,6‐dihydro‐2<i>H</i>‐pyran (Nerol oxide) and Natural Occurrence of its Racemate

Abstract

Abstract Following a known procedure, a mixture of (−)‐(2 S ,3 R )‐ and (+)‐(2 R ,3 R )‐2,3‐epoxy‐citronellols ( 5 ) was prepared from (−)‐( R )‐linalool ( 3 ) via epoxy alcohol 4 and then reduced to (−)‐( R )‐3‐hydroxy‐citronellol ( 6 ). Sensitized photooxygenation of (−)‐( R )‐diol 6 led in part to (−)‐( R )‐triol 8 which was cyclodehydrated by dilute acid to a mixture of diastereoisomeric tetrahydropyran‐4‐ols 9 and 10 . Dehydration of hydroxy ethers 9 and 10 afforded (−)‐( S )‐nerol oxide ( 11 ) and (+)‐( R )‐nerol oxide ( 12 ), respectively, with an optical purity of 91%. Nerol oxide isolated from Bulgarian rose oil (0.038%) proved to be racemic. These results shed some light on the formation of nerol oxide in plants.