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Entropy-controlled Selectivity in the Vinylation of a Cyclic Chiral Nitrone. An Efficient Route to Enantiopure Polyhydroxylated Pyrrolidines

Entropy-controlled Selectivity in the Vinylation of a Cyclic Chiral Nitrone. An Efficient Route to Enantiopure Polyhydroxylated Pyrrolidines

M Lombardo, S Fabbroni, C Trombini

J Org Chem. 2001 Feb 23;66(4):1264-8.

PMID: 11312956

Abstract:

A short synthesis of 1,4-dideoxy-1,4-imino-L-arabinitol (LAB1) (4) and of 1,4-dideoxy-1,4-imino-D-galactitol (5), two azasugars active as enzymatic inhibitors, is reported. The key reaction is the addition of vinylmagnesium chloride to (3S,4S)-3,4-bis(benzyloxy)-3,4-dihydro-2H-pyrrole 1-oxide (3), a nitrone easily available from L-tartaric acid. Unexpectedly, the reaction affords the corresponding (2S,3S,4S)-1-hydroxy-2-ethenyl-3,4-bis(benzyloxy)pyrrolidine (9) in very good yield and in 93/7 diastereomeric ratio (dr) independently of the reaction temperature, thus representing a unique case of entropy-controlled reaction in a 100 K interval (from +20 degrees C to -80 degrees C). The trans intermediate 9 is converted in two steps (reduction, N-protection) into the common intermediate (2S,3S,4S)-1-(benzyloxycarbonyl)-3,4-bis(benzyloxy)-2-ethenylpyrrolidine (11). Double bond oxidation followed by reductive debenzylation opens a route to the target pyrrolidine azasugars 4 and 5.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
LS7931201	2,4-bis(benzyloxy)pyrimidine-5-boronic acid			Price

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