The reproducible enantioselective saponification of the corresponding diacetates with pig liver esterase (PLE) gave monoacetates ( 25a-c) of >95% ee. tarns, trans -2- Nitrocyclohexane-1,3-diol ( 23a), 3,4,5,6-tetrahydro-4-nitro-2 H-pyran-3,5-diol ( 23b), 4-ni- trothiane-3,5-diol ( 23c) and some of their derivatives ( Scheme 4) were easily prepared from methanolic solutions of the starting dialdehydes and nitromethane or nitroethane (1.5 equiv.) in the presence of cata-lytic amounts of 2 M NaOH and then converted into the corresponding diacetates ( 24a-c). The pioneering studies of Fisher and Lichtenthaler were useful to Seebach and coworkers 45 in the preparation of enantiomerically pure derivatives of cyclic 2-nitroallylic alcohols, which are important chiral multiple coupling reagents. This compound represented a useful system for model studies of synthetic and stereochemical problems implicated in the more complex chemistry of nitro sugars. In the case of glutaraldehyde and nitromethane, nitrodiol ( 22 equation 6) was readily obtained as a single trans, trans diastereomer. 7,9 Three-atom tethers offer the best results.
This reaction leads to five-, six- and seven-membered rings and is equally applicable to aliphatic, aromatic and sugar dialdehydes. This sequence consists of a cyclization process where a faster intramolecular nitroaldol reaction follows the first intermolecular one and the methyl group of the nitromethane is incorporated into the ring. Two consecutive nitroaldol reactions were observed when nitromethane, or one of its higher homologs, was treated with 1,4-, 1,5- and 1,6-dialdehydes in the presence of catalytic or stoichiometric amounts of a base.
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