‘Syn-effect’ in the diastereoselective alkylation of 3-[(E)-α,β-unsaturated-γ-substituted]-N-acyloxazolidinones
摘要:
Synthetic methods for the formation of alkenes usually produce the E-alkene because it is more stable. However, in isomerization reaction (double bond migration) that takes place in alpha, beta-unsaturated carbonyl compounds, when these carbonyl compounds are exposed to strong bases, furnish Z-alkenes highly stereoselective depending on the gamma-substituent in the alpha, beta-unsaturated carbonyl. This stereo-selectivity can be attributed to the known Syn-effect. The synthetic value of this methodology is the achievement of chiral alcohol bearing an electron rich Z-alkene, as well as substituted, which was accomplished via removal of the oxazolidinone moiety under treatment with NaBH4, THF-H2O. (C) 2015 Elsevier Ltd. All rights reserved.
Diastereoselective alkylations of oxazolidinone vinylogous glycolates
摘要:
A highly Z-selective isomerization (double bond migration) was observed when oxazolidinone vinylogous glycolate was exposed to a strong base to give N-acyl oxazolidinone, bearing an electron rich olefin. The corresponding enolate was exposed to alkyl halides to provide alkylated compounds on the gamma-position with respect to OBn group, with high regioselectivity and moderate diastereoselectivity. However, the nature of the chiral oxazolidinone leads to a significant increase in the reaction diastereoselectivity. A stereospecific formation of cis-olefin was also observed in these alkylated compounds. (c) 2012 Elsevier Ltd. All rights reserved.