Prochiral Diols Research Articles

Catalytic Atroposelective Aerobic Oxidation Approaches to Axially Chiral Molecules.

A copper and chiral nitroxide co-catalyzed aerobic enantioselective oxidation process has been developed that allows access to axially chiral molecules. Two complementary atroposelective approaches, oxidative kinetic resolution (OKR) and desymmetrization, were studied using ambient air as the stoichiometric terminal oxidant. OKR of rac-N-arylpyrrole alcohols and rac-biaryl alcohols affords the optically pure compounds with er up to 3.5:96.5 and 5.5:94.5, respectively. Desymmetrization of prochiral diols provides axially chiral biaryl compounds with er up to 99:1.

Desymmetrization of Diols by Phosphorylation with a Titanium-BINOLate Catalyst.

The desymmetrization of ten prochiral diols by phosphoryl transfer with a titanium-BINOLate complex is discussed. The phosphorylation of nine 1,3-propane diols is achieved in yields of 50-98%. Enantiomeric ratios as high as 92:8 are achieved with diols containing a quaternary C-2 center incorporating a protected amine. The chiral ligand, base, solvent, and stoichiometry are evaluated along with a nonlinear effect study to support an active catalyst species that is oligomeric in chiral ligand. The use of pyrophosphates as the phosphorylating agent in the desymmetrization facilitates a user-friendly method for enantioselective phosphorylation with desirable protecting groups (benzyl, o-nitrobenzyl) on the phosphate product.

Total synthesis of (–)-brazilane via a lipase-catalyzed desymmetrisation reaction

Herein, we described the asymmetric total synthesis of (–)-brazilane, an optically active natural product. The key steps of this synthetic approach are a lipase-catalyzed desymmetrisation reaction of a prochiral diol using vinyl acetate to prepare a chiral primary alcohol and a trifluoroacetic acid-catalyzed one pot intramolecular tandem Prins/Friedel-Crafts reaction used to construct the cis-fused chromane and indane framework.

Enantioselective Desymmetrization of 2-Aryl-1,3-propanediols by Direct O-Alkylation with a Rationally Designed Chiral Hemiboronic Acid Catalyst That Mitigates Substrate Conformational Poisoning.

Enantioselective desymmetrization by direct monofunctionalization of prochiral diols is a powerful strategy to prepare valuable synthetic intermediates in high optical purity. Boron acids can activate diols toward nucleophilic additions; however, the design of stable chiral catalysts remains a challenge and highlights the need to identify new chemotypes for this purpose. Herein, the discovery and optimization of a bench-stable chiral 9-hydroxy-9,10-boroxarophenanthrene catalyst is described and applied in the highly enantioselective desymmetrization of 2-aryl-1,3-diols using benzylic electrophiles under operationally simple, ambient conditions. Nucleophilic activation and discrimination of the enantiotopic hydroxy groups on the diol substrate occurs via a defined chairlike six-membered anionic complex with the hemiboronic heterocycle. The optimal binaphthyl-based catalyst 1g features a large aryloxytrityl group to effectively shield one of the two prochiral hydroxy groups on the diol complex, whereas a strategically placed "methyl blocker" on the boroxarophenanthrene unit mitigates the deleterious effect of a competing conformation of the complexed diol that compromised the overall efficiency of the desymmetrization process. This methodology affords monoalkylated products in enantiomeric ratios equal or over 95:5 for a wide range of 1,3-propanediols with various 2-aryl/heteroaryl groups.

Syntheses and odor properties of optically active dimethyl octenone and its analogs

The optically active isomers of dimethyl octenone, which is used in citrus accords, and its analogs, were synthesized from a common chiral intermediate prepared by the lipase-catalyzed desymmetrization of prochiral diol. The results of an olfactory evaluation of the prepared isomers are also reported.

ChemInform Abstract: Aerobic Oxidative Desymmetrization of meso‐Diols with Bifunctional Amidoiridium Catalysts Bearing Chiral N‐Sulfonyldiamine Ligands.

Abstract Asymmetric aerobic oxidation of a range of meso - and prochiral diols with chiral bifunctional Ir catalysts is described. A high level of chiral discrimination ability of Cp ∗ Ir complexes derived from ( S , S )-1,2-diphenylethylenediamine was successfully demonstrated by desymmetrization of secondary benzylic diols such as cis -indan-1,3-diol and cis -1,4-diphenylbutane-1,4-diol, providing the corresponding ( R )-hydroxyl ketones with excellent chemo- and enantioselectivities. Enantiotopic group discrimination in oxidation of symmetrical primary 1,4- and 1,5-diols gave rise to chiral lactones with moderate ees under similar aerobic conditions.

Aerobic oxidative desymmetrization of meso-diols with bifunctional amidoiridium catalysts bearing chiral N-sulfonyldiamine ligands

Asymmetric aerobic oxidation of a range of meso- and prochiral diols with chiral bifunctional Ir catalysts is described. A high level of chiral discrimination ability of Cp∗Ir complexes derived from (S,S)-1,2-diphenylethylenediamine was successfully demonstrated by desymmetrization of secondary benzylic diols such as cis-indan-1,3-diol and cis-1,4-diphenylbutane-1,4-diol, providing the corresponding (R)-hydroxyl ketones with excellent chemo- and enantioselectivities. Enantiotopic group discrimination in oxidation of symmetrical primary 1,4- and 1,5-diols gave rise to chiral lactones with moderate ees under similar aerobic conditions.

Lipase-catalyzed preparation of optically active isomers of cyclamen aldehyde

Abstract The optically active isomers of cyclamen aldehyde 1a were synthesized from a chiral intermediate prepared by lipase-catalyzed enantioselective transesterification of a prochiral diol with vinyl acetate. The absolute configuration of the enantiomer of 1a with dextrorotatory in chloroform was determined to be ( S )-configuration. The results of an olfactory evaluation of the prepared isomers are also reported.

Laboratory Evolution of Enantiocomplementary Candida antarctica Lipase B Mutants with Broad Substrate Scope

Candida antarctica lipase B (CALB) is a robust and easily expressed enzyme used widely in academic and industrial laboratories with many different kinds of applications. In fine chemicals production, examples include acylating kinetic resolution of racemic secondary alcohols and amines as well as desymmetrization of prochiral diols (or the reverse hydrolytic reactions). However, in the case of hydrolytic kinetic resolution of esters or esterifying kinetic resolution of acids in which chirality resides in the carboxylic acid part of the substrate, rate and stereoselectivity are generally poor. In the present study, directed evolution based on iterative saturation mutagenesis was applied to solve the latter problem. Mutants with highly improved activity and enantioselectivity relative to wild-type CALB were evolved for the hydrolytic kinetic resolution of p-nitrophenyl 2-phenylpropanoate, with the selectivity factor increasing from E = 1.2 (S) to E = 72 (S) or reverting to E = 42 (R) on an optional basis. Surprisingly, point mutations both in the acyl and alcohol pockets of CALB proved to be necessary. Some of the evolved CALB mutants are also efficient biocatalysts in the kinetic resolution of other chiral esters without performing new mutagenesis experiments. Another noteworthy result concerns the finding that enantiocomplementary CALB mutants for α-substituted carboxylic acid esters also show stereocomplementarity in the hydrolytic kinetic resolution of esters derived from chiral secondary alcohols. Insight into the source of stereoselectivity was gained by molecular dynamics simulations and docking experiments.

Asymmetric Bis(alkoxycarbonylation) Reaction of Cyclic Olefins Catalyzed by Palladium in the Presence of Copper(I) Triflate

Abstract A palladium-catalyzed asymmetric bis(alkoxycarbonylation) reaction of 1,2-dihydronaphthalenes and related cyclic olefins in the presence of copper(I) triflate was achieved by using a chiral bioxazoline ligand under normal pressure of carbon monoxide and oxygen to give the corresponding optically active cis-dicarboxylates with enantioselectivities up to 94% ee. An asymmetric intra- and intermolecular bis(alkoxycarbonylation) reaction of a prochiral diol possessing dihydronaphthalene skeleton also proceeded enantioselectively by an appropriate selection of the substituent of bioxazoline ligand. The carbonylation product derived from 8-methoxy-1,2-dihydronaphthalene was applied to the synthesis of a biologically active hexahydrobenz[e]isoindole derivative.

Complementary Lipase-Mediated Desymmetrization Processes of 3-Aryl-1,5-Disubstituted Fragments. Enantiopure Synthetic Valuable Carboxylic Acid Derivatives

Desymmetrizaton enzymatic processes have been extensively studied searching for optimal methods of producing enantioenriched monoacetates from prochiral diols and diesters. AK lipase has been found as an excellent biocatalyst for the desymmetriaztion of a series of previously synthesized 3-arylpentane-1,5-diols derivatives. The access to (S)- or (R)-monoacetates in high optical purity (86-99% ee) has been possible by using acetylation or hydrolysis reactions, respectively, where the reaction parameters have been optimized in terms of source and amount of biocatalyst, temperature, solvent, and reaction time. The synthetic potential of enantiopure monoesters has been demonstrated by using these interesting chiral building blocks for the preparation of novel enantiopure carboxylic acid derivatives.

Lipase-mediated preparation of optically active isomers of Rosaphen®

The optically active isomers of Rosaphen® (RS)-1 were synthesized from the chiral intermediate prepared by lipase-catalyzed desymmetrization of prochiral diol. The results of an olfactory evaluation of the prepared isomers are reported.

Experimental and DFT study of 2-ferrocenylpropan-2-ol cyclodimerization products

Abstract 1,1′-(1-Ferrocenyl-1,3,3-trimethylpropane-1,3-diyl)ferrocene and 1,2-(1-ferrocenyl-1,3,3-trimethylpropane-1,3-diyl)ferrocene are formed as cyclodimeric products during the synthesis of β-ferrocenyl carbinols, in relative ratios which depend on the reaction conditions. Their ratios and stabilities are examined, and calculated at the BP86 level of theory and several different isomers of the homoannular product were examined by DFT calculations. Keywords : Ferrocene, cyclodimeric products, carbinols, DFT calculation Introduction Ferrocenyl alcohols are very useful synthetic intermediates in the synthesis of many biologically active compounds, industrially important compounds, as ligands in homogenous catalysis, in material science ( e.g . in nonlinear optics) and in bio-organometallic chemistry as redox-active probes or candidates for drugs. 1,2 In a previous paper 3 we studied the nucleophilic substitution of diethyl malonate with ω-ferrocenylalkanols, derived carbinyl acetates, bromides and quaternary salts to α-ferrocenylalkylmalonates. These substrates can easily be reduced into the prochiral 2-(ω-ferrocenylalkyl)propane-1,3-diols. Furthermore, we examined the enzymatic esterification of these prochiral diols in order to determine a degree of desymmetrization depending on the length of the side chain,

Gem-Difluorocyclopropane as core molecule candidate for liquid crystal compounds

The synthesis of a novel chiral gem-difluorocyclopropane building block has been accomplished using chemo-enzymatic reaction protocol; the prochiral diol of 1,4-bis(2,2-difluoro-3-(hydroxymethyl)cyclopropyl)benzene ( 5) was converted to the corresponding chiral diacetate by Pseudomonas lipase (lipase SL-25, Meito)-catalyzed transesterification with vinyl acetate as acyl donor with >99% enantiomeric excess. Various types of diesters or dialkyl ether were prepared from the diol and their helical twisting power (HTP) was evaluated by addition of 1.0 wt% to a non-chiral nematic liquid crystal host; the HTP was significantly dependent on the structure of ester or ether moieties and diester of diol 5 with isopropylfumalic acid showed the largest HTP.

Monoacetylation of Prochiral Amino-2-alkyl-1,3-propanediols

The authors report a non-enzymatic approach to monoacetylation of prochiral diols giving 70-88% ee. They utilize a chiral sulfon­amide-Zn complex as catalyst. The use of Trost’s catalyst for the monobenzoylation of pro­chiral 1,3-diols was attempted (B. M. Trost, T. Mino J. Am. Chem. Soc. 2003, 125, 2410-2411) but gave only 10% ee. The difficulty is believed to be due to the presence of the quaternary prochiral center. The use of the Zn-bridged bis(sulfonamide) catalyst proved to be efficacious for this reaction.

( R)-4-Hydroxymethyl-2-phenyl-4,5-dihydrooxazol-4-ylmethyl acetate: chiral building block for the synthesis of optically active α-substituted α-amino acid derivatives

( R)-4-Hydroxymethyl-2-phenyl-4,5-dihydrooxazol-4-ylmethyl acetate was efficiently obtained by lipase-catalyzed asymmetrization of the prochiral diol. ( R)-4-Hydroxymethyl-2-phenyl-4,5-dihydrooxazol-4-ylmethyl acetate was converted to ( R)-2-(hydroxymethyl)glutamic acid and a synthetic intermediate of (−)-deoxydysibetaine.

Enantiodivergent preparation of optically active oxindoles having a stereogenic quaternary carbon center at the C3 position via the lipase-catalyzed desymmetrization protocol: effective use of 2-furoates for either enzymatic esterification or hydrolysis.

Both enantiomers of oxindoles 2a-h, having a stereogenic quaternary carbon center at the C3 position and a different N-protective group, were readily prepared by the lipase-catalyzed desymmetrization protocol. Thus, the transesterification of the prochiral diols 3a-h with 1-ethoxyvinyl 2-furoate 5 was catalyzed by Candida rugosa lipase to give (R)-(+)-2a-h (68-99% ee), in which the use of a mixed solvent, (i)Pr(2)O (diisopropyl ether)-THF, was crucial. The same lipase also effected the enantioselective hydrolysis of the difuroates 4a-h in a mixture of (i)Pr(2)O, THF, and H(2)O to provide the enantiomers (S)-(-)-2a-h (82-99% ee). The products 2 obtained by both methods were stable against racemization. These enzymatic desymmetrization reactions were also applicable for other typical symmetrical difuroates 12b and 15b to provide the racemization-resistant products 13b and 16b.

Effective asymmetric synthesis of 1,2,9,9a-tetrahydrocyclopropa[c]benzo[e]indol-4-one (CBI).

A short, asymmetric synthesis of the 1,2,9,9a-tetrahydrocyclopropa[c]benzo[e]indol-4-one (CBI) analogue of the CC-1065 and duocarmycin alkylation subunits is detailed that employs an effective enzymatic desymmetrization reaction of prochiral diol 12 using a commercially available Pseudomonas sp. lipase. The optically active monoacetate (S)-13 is furnished in exceptional conversions (88%) and optical purity (99% ee) and serves as an intermediate for the preparation of either enantiomer of CBI. Similarly, the Pseudomonas sp. lipase resolved the racemic intermediate 19, affording advanced intermediates of CBI in good conversions and optical purity (99% ee), and provided an alternative approach to the preparation of optically active CBI derivatives.

Enantioselective preparation of asymmetrically protected 2-propanoyl-1,3-propanediol derivatives: toward the total synthesis of Kazusamycin A

The preparation of enantiomerically pure 2-propanoyl-1,3-propanediol derivatives, key intermediates in our studies on total synthesis of the potent antitumor compound Kazusamycin A are described. After various enzymatic protocols for desymmetrization of the prochiral diol were studied, it was found that these compounds could be prepared in 97–98% ee by means of an enzymatic kinetic resolution.

Efficient synthesis of ( R)- and ( S)-1-amino-2,2-difluorocyclopropanecarboxylic acid via lipase-catalyzed desymmetrization of prochiral precursors

The asymmetric syntheses of (+)-( R)-1-amino-2,2-difluorocyclopropane-1-carboxylic acid and its enantiomer have been accomplished. Key reactions in the synthetic design are lipase-catalyzed desymmetrization of a prochiral diol and a prochiral diacetate.