Esters hydrobromination

Chiral differentiation between enantiomeric amino acid / -nitrophenyl ester hydrobromines was observed [9,73] in transacylations catalysed by the chiral 3,3-... 

The starting amino acid for nylon-11 is produced from methyl ricinoleate [141 -24-2] which is obtained from castor oil (qv). The methyl ricinoleate is pyrolized to methyl 10-undecylenate [25339-67-7] and heptanal [111-71-7]. The unsaturated ester is hydroly2ed and then converted to the amino acid by hydrobromination, followed by ammoniation and acidification. The CO-amino acid product is a soft paste containing water, which is dried in the first step of the polymeri2ation process. 

Hydrobromination of the same substrate in the a-cyclodextrin complex gave the monobromide with the opposite configuration at 46 % e.e.. This clearly shows that ethyl trans-cinnamate forms complexes with a- and 3-cyclodextrins such that the anti-addition of hydrogen bromide occurs with high but different enantioselectivities in the two cases to yield monobromide derivatives of opposite chiralities. A detailed mechanism, however, could not be described at the present time for the observed asymmetric induction in the hydrobromination and bromination of the a-cyclodextrin complex, because no crystalline or molecular structures were determined for the ester included in a-cyclodextrin. 

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