Chiral Formyl Anion Equivalents Research Articles

Enantioselective Reaction of ?-Lithiated Thiazolidines as New Chiral Formyl Anion Equivalents.

Abstract The reaction of lithiated N-Boc-thiazolidine and N-Boc-benzothiazolidine with benzophenone in the presence of (−)-sparteine afforded the products with up to 97% ee and 93% ee, respectively. The reaction with various aromatic and aliphatic aldehydes also afforded the products with high enantioselectivity and moderate diastereoselectivity. Each diastereomer could be converted to optically active diols. Consequently, lithiated N-Boc-thiazolidine and N-Boc-benzothiazolidine serve as chiral formyl anion equivalents. The reaction was confirmed to proceed through a dynamic thermodynamic resolution pathway.

Enantioselective Reaction of α‐Lithiated Thiazolidines as New Chiral Formyl Anion Equivalents.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Highly Enantioselective Reaction of Lithiated N‐Boc‐thiazolidine: A New Chiral Formyl Anion Equivalent.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Enantioselective reaction of α-lithiated thiazolidines as new chiral formyl anion equivalents

The reaction of lithiated N-Boc-thiazolidine and N-Boc-benzothiazolidine with benzophenone in the presence of (−)-sparteine afforded the products with up to 97% ee and 93% ee, respectively. The reaction with various aromatic and aliphatic aldehydes also afforded the products with high enantioselectivity and moderate diastereoselectivity. Each diastereomer could be converted to optically active diols. Consequently, lithiated N-Boc-thiazolidine and N-Boc-benzothiazolidine serve as chiral formyl anion equivalents. The reaction was confirmed to proceed through a dynamic thermodynamic resolution pathway.

Enantioselective Reaction of α‐Lithiated Dithioacetals Using Chiral Bis(oxazoline)s: New Chiral Formyl Anion Equivalents.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Highly enantioselective reaction of lithiated N-Boc-thiazolidine: a new chiral formyl anion equivalent.

Reaction of lithiated N-Boc-thiazolidine with various aldehydes in the presence of (-)-sparteine afforded the products with up to 93% ee. The reaction was confirmed to proceed through a dynamic thermodynamic resolution pathway. Each diastereomeric alcohol could be converted to the corresponding optically active 1,2-ethanediols.

ChemInform Abstract: Lithiated 4‐Isopropyl‐3‐(methylthiomethyl)‐5,5‐diphenyloxazolidin‐2‐one: A Chiral Formyl Anion Equivalent for Enantioselective Preparations of 1,2‐Diols, 2‐Amino Alcohols, 2‐Hydroxy Esters, and 4‐Hydroxy‐2‐alkenoates.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Lithiated 4-isopropyl-3-(methylthiomethyl)-5,5-diphenyloxazolidin-2-one: a chiral formyl anion equivalent for enantioselective preparations of 1,2-diols, 2-amino alcohols, 2-hydroxy esters, and 4-hydroxy-2-alkenoates.

The heterocyclic compound specified in the title (and readily prepared from commercial precursors) has a sterically protected C==O group, so that direct lithiation by BuLi at the exocyclic CH(2) group is possible (3 --> Li-3). The lithiated N,S-acetal derivative (Li-3) adds diastereoselectively to aldehydes (Table 2), unsymmetrical ketones (Table 3), chalcone (1,4-addition, Scheme 2), and N-phosphinoyl- and N-sulfonylimines (Table 4). Protection of the newly formed OH groups (Scheme 3) and/or MeS/OH displacement by Hg(O(2)CCF(3))(2) in aqueous THF/acetonitrile converts the N,S-acetals into hemiaminals (--> 20) which, in turn, are readily cleaved to aldehydes, with recovery of the chiral auxiliary (1, Scheme 4). The aldehydes (especially those lacking alpha-carbonyl hydrogens) may be isolated, or they are trapped in situ by reduction to (selectively protected) diols or amino alcohols, by addition of Grignard or Li reagents, which provides diols with two stereogenic centers, by oxidation to give 2-hydroxy esters, or by olefination to provide 4-hydroxy-2-alkenoates (Scheme 5). The scope and limitations of the new, overall enantioselective transformation are determined, and the readily recovered chiral auxiliary used is compared with oxazolidinones of other substitution patterns (Scheme 7). The configuration of a number of products has been assigned by single-crystal X-ray diffraction (cf. Figure 5). These structures and similarities of NMR data led to configurational assignment of the other products (see formulas in the schemes and tables) by analogy. A simple mechanistic model for the stereochemical course of the addition of Li-3 to aldehydes and ketones is presented (Figure 6).

ChemInform Abstract: Formation and Reaction of 2‐Metalated N‐Boc‐4,4‐dimethyl‐1,3‐oxazolidines in the Presence of (‐)‐Sparteine: New Chiral Formyl Anion Equivalents.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Formation and reaction of 2-metalated N-Boc-4,4-dimethyl-1,3-oxazolidines in the presence of (−)-sparteine: new chiral formyl anion equivalents

Lithiation of N-Boc-4,4-dimethyl-1,3-oxazolidine with s-BuLi and the following reaction with benzaldehyde was carried out in the presence of (−)-sparteine. The reaction was not diastereoselective ( syn: anti=46:54), but each isomer of the adducts was obtained enantioselectively ( syn: 90% ee, anti: 88% ee). Addition of MgBr 2 to the reaction mixture increased the diastereoselectivity to syn: anti=90:10.