Reinvestigation of the alkylation of pyroglutamate ester urethanes
1998; Elsevier BV; Volume: 39; Issue: 15 Linguagem: Inglês
10.1016/s0040-4039(98)00174-9
ISSN1873-3581
AutoresJean‐Damien Charrier, J. Emmett Duffy, Peter B. Hitchcock, Douglas W. Young,
Tópico(s)Asymmetric Synthesis and Catalysis
ResumoPrevious studies by several groups on the alkylation of pyroglutanic acid derivatives have led to a consensus that the stereoselectivity of alkylation at C-4 is invariably trans to the ester group at C-2. We have now discovered that this generalisation is not invariably correct and that, although for Sn1-type electrophiles stereoselectivity is in fact trans. Sn2-type electrophiles the thermodynamically less stable cis products with high diastereoselectivity. Use of the bulky proton source 2,6-di-tert-butylphenol to quench these reactions yields cis isomers as the only products in good yield, thus making direct alkylation of pyroglutamic acid derivatives a useful starting point for the synthesis of homochiral target compounds.
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