Allylic glycolate esters Ireland-Claisen rearrangement

Claisen rearrangement of glycolates. Two laboratories 2 have reported that allylic glycolate esters undergo Claisen-Ireland rearrangement (6, 276-277) with useful diastereoselectivity. This rearrangement was used in a synthesis of 1, the aggregation pheromone of the European elm bark beetle.1... 

In contrast to the extensive use of glycolate esters, lactate, mandelate and other higher a-oxygenated esters have been used much less frequently. Early work by Bartlett et al. showed that the Ireland-Claisen rearrangement could be used to prepare allylated lactic acids in good yield, but the diastereoselectivity was disappointingly low (Scheme 4.75) [20]. 

The Ireland-Claisen rearrangement is not limited to allylic esters, but can also be applied to propargylic glycolates [14]. In the rearrangement of several pro-pargylic esters 14 the diastereoselectivity (ds), the allenic a-hydroxyacids 15 are formed with, was always very high (Scheme 5.2.6, Table 5.2.3). In this reaction, LHMDS in THF is the best base/solvent combination, LDA gave no desired product, and the use of ether and dimethoxyethane resulted in a decrease of both yield and diastereoselectivity. 

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