92053-24-2Relevant academic research and scientific papers
Highly stereoselective alkylation of (S)-proline-based chiral auxiliaries
Andersson, Fredrik,Hedenstroem, Erik
, p. 2539 - 2545 (2004)
Alkylation reactions with switching diastereoselectivity depending on the R1 group, resulting in a dr of up to 99:1. Alkylation of the enolates of the propanoylamides of two chiral auxiliaries (S)-(-)-2-(pyrrolidin-2-yl) propan-2-ol 1a and (S)-(-)-2-(2-methoxypropan-2-yl)pyrrolidine 1b, derived from (S)-proline, with benzyl bromide and n-butyl iodide has been studied. The auxiliaries 1a and 1b induced opposite selectivity that is (R)- and (S)-configuration, respectively, at the newly created stereogenic centre. The diastereoselectivities and conversion yields in these alkylations were moderate to excellent. When Cp2ZrCl2 was used as an enolate coordinating agent, benzylation of propanoylated 1b gave an excellent diastereomeric ratio of 99:1. The benzylated diastereomeric products from either propanoylated 1a or 1b were easily separated by liquid chromatography.
Asymmetric Synthesis of 2-Alkylalkanoic Acids via Alkylation of Chiral Amide Anions
Guoqiang, Lin,Hjalmarsson, Mats,Hoegberg, Hans-Erik,Jernstedt, Karen,Norin, Torbjoern
, p. 795 - 802 (2007/10/02)
Acylation of (S)-proline methyl ester (2) gave amide ester 3 (R1=alkyl), which on reaction with methylmagnesium iodide furnished the tertiary alcohol 4.Alkylation of the dianion from this yielded mainly one diastereomer of the amide 5, which on acid hydrolysis gave the chiral 2-alkylalkanoic acid 6 in 75-90 percent e.e. and 55-82 percent chemical yield from the hydroxyamide 4.The latter compound could be recovered from the hydrolysate with preserved optical purity via acylation without isolation of the tertiary prolinol 7.The diastereomeric mixture of amides 5' and 5" could be separated by column chromatography leading to the acid 6 in very high optical purity.
