Limonene introduction

Liu et al. have reported on the total synthesis of 182 and 239 to verify their structural relationship and to confirm the relative and absolute configurations.The overall strategic plan involves (1) chemical conversion of epoxy alcohol 182 to lactone 239 via an intramolecular lactonization, (2) construction of the 14-membered cembrane ring with geometrically defined double bonds and substiments, (3) implementation of C-1 stereogenic center via a readily available chiral pool (i.e., 5-limonene), and (4) introduction of chiral epoxide functionality via a Sharpless... 

The role of acidity is emphasized when an OH group is present in the limonene structure (reaction lb) [23]. The acidity of the carrier must then be strongly reduced to avoid dehydration. Carriers such as carbon, silica, and alumina are appropriate, although other forms than y-Al203 are usually used. The introduction of a base such as triethylamine directly into the reaction mixture is also imperative. Considering these restrictions, the temperature of the reaction must not exceed 150°C. Thus, it is essential to reduce the pressure (< 0.01 bar) to increase the yield. 

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