0000000000464908
AUTHOR
Encarnación Castillo
ChemInform Abstract: Diastereoselectivity in Organometallic Additions to the Carbonyl Group of Protected Erythrulose Derivatives.
We have investigated a number of nucleophillic additions to l-erythrulose derivatives (4−12) bearing protective O-silyl, O-benzyl, and O-trityl groups in various relative positions. The results are discussed in the frame of chelated vs nonchelated transition states with additional support of previously published theoretical calculations. Sound evidence appears to exist for the formation of α-chelates as the key intermediates in nucleophillic additions to these α,β-dioxygenated ketones. Since such evidence is still lacking in the case of β-chelates, proposals of their intermediacy have been relegated in favor of the more solid Felkin−Anh model, which predicts the same stereochemical result. …
Boron aldol additions with erythrulose derivatives: dependence of stereoselectivity on the type of protecting group
Abstract Boron aldol additions of 1- O -silylated 3,4-di- O -benzyl- and 3,4-di- O -benzoyl- l -erythrulose and achiral aldehydes using dicyclohexylboron chloride have been investigated. The dibenzyl derivative gave syn/syn stereoisomers with high stereoselectivity, whereas the dibenzoyl derivative gave syn/anti stereoisomers. It is believed that, while the dibenzoyl erythrulose gives rise to the E enolate in the presence of dicyclohexylboron chloride, as usually observed with this reagent, only the Z enolate is formed in the case of the dibenzyl derivative.
ChemInform Abstract: A Stereoselective Synthesis of (+)-Malyngolide via a Ring-Closing Olefin Metathesis.
Abstract A very short and stereoselective synthesis of the non-natural enantiomer of malyngolide from l -erythrulose is described. Key features of the synthesis are the Felkin–Anh diastereoselective allylation of a polyoxygenated ketone and the allylation/metathesis/allylic oxidation protocol recently described by our group.
ChemInform Abstract: Boron Aldol Additions with Erythrulose Derivatives: Dependence of Stereoselectivity on the Type of Protecting Group.
Abstract Boron aldol additions of 1- O -silylated 3,4-di- O -benzyl- and 3,4-di- O -benzoyl- l -erythrulose and achiral aldehydes using dicyclohexylboron chloride have been investigated. The dibenzyl derivative gave syn/syn stereoisomers with high stereoselectivity, whereas the dibenzoyl derivative gave syn/anti stereoisomers. It is believed that, while the dibenzoyl erythrulose gives rise to the E enolate in the presence of dicyclohexylboron chloride, as usually observed with this reagent, only the Z enolate is formed in the case of the dibenzyl derivative.
A stereoselective synthesis of (+)-malyngolide via a ring-closing olefin metathesis
Abstract A very short and stereoselective synthesis of the non-natural enantiomer of malyngolide from l -erythrulose is described. Key features of the synthesis are the Felkin–Anh diastereoselective allylation of a polyoxygenated ketone and the allylation/metathesis/allylic oxidation protocol recently described by our group.
Diastereoselectivity in Organometallic Additions to the Carbonyl Group of Protected Erythrulose Derivatives
We have investigated a number of nucleophillic additions to L-erythrulose derivatives (4-12) bearing protective O-silyl, O-benzyl, and O-trityl groups in various relative positions. The results are discussed in the frame of chelated vs nonchelated transition states with additional support of previously published theoretical calculations. Sound evidence appears to exist for the formation of alpha-chelates as the key intermediates in nucleophillic additions to these alpha,beta-dioxygenated ketones. Since such evidence is still lacking in the case of beta-chelates, proposals of their intermediacy have been relegated in favor of the more solid Felkin-Anh model, which predicts the same stereoche…