Chiral Carbonates Research Articles

Efficient Two‐Step Conversion of α,β‐Unsaturated Aldehydes to Optically Active γ‐Oxy‐α,β‐unsaturated Nitriles and Its Application to the Total Synthesis of (+)‐Patulolide C.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Palladium-catalyzed enantiospecific reaction of propargylic carbonates with phenols: cascade chirality transfer.

[reaction: see text] A cascade chirality transfer process has been achieved by the palladium-catalyzed reaction of substituted propargylic carbonates with phenols. The reaction proceeds in a highly enantiospecific manner to produce chiral cyclic carbonates, which supports the existence of the pi-propargylpalladium intermediate in the reaction mechanism. The (E)- and (Z)-selectivity of the products can be controlled by choice of the phosphine ligand.

Efficient two-step conversion of alpha,beta-unsaturated aldehydes to optically active gamma-oxy-alpha,beta-unsaturated nitriles and its application to the total synthesis of (+)-patulolide C.

[reaction: see text] An efficient two-step conversion of alpha,beta-unsaturated aldehydes into optically active gamma-oxy-alpha,beta-unsaturated nitriles is described. First, catalytic asymmetric cyanation-ethoxycarbonylation using (S)-YLi(3)tris(binaphthoxide) (YLB) afforded chiral allylic cyanohydrin carbonate. Second, a [3,3]-sigmatropic rearrangement proceeded without racemization under thermal conditions to give gamma-oxy-alpha,beta-unsaturated nitriles. Lewis acids were also effective for the rearrangement, and the reaction proceeded smoothly under mild conditions. To demonstrate the utility of the conversion, concise catalytic enantioselective total synthesis of (+)-patulolide C was performed.

Stereoregular Poly(N-propargylcarbamates) Having Helical Conformation Stabilized by the Intramolecular Hydrogen Bonds

N-Propargylcarbamates (2, HC⋮CCH2NHCO2R), where R = i-Bu (2a) or (S)-CH2CH(CH3)C2H5 (2b), were polymerized in the presence of a Rh catalyst, [(nbd)RhCl]2−Et3N, in CHCl3, giving stereoregular cis polymers as slightly yellow solids in good yields. The 1H NMR spectra of poly(2) showed very broad signals at ambient temperature, indicating the limited mobility of the main chain. IR spectroscopic study of the polymers in CHCl3 revealed that most of the pendant carbamate groups participate in intramolecular hydrogen bonds. The chiral polymer from 2b exists in a helical conformation with an excess of one-handed screw sense, which was supported by the very large optical rotation ([α]D = +777°) and intense CD effects ([θ]max = 81 700 deg cm2 dmol-1). A Rh-based polymer from the corresponding chiral carbonate monomer, (S)-HC⋮CCH2OCO2CH2CH(CH3)C2H5 (3), obtained as a viscous oil, showed much poorer chiroptical properties ([α]D = +13.8°), meaning that the intramolecular hydrogen bonds rigidify the polymer backbone and simultaneously induce and stabilize the helical conformation of poly(2). The contribution of the hydrogen bonds to the secondary structure was also supported by variation in the CD and UV−vis spectra of poly(2) upon the addition of methanol.

Synthesis of Calix[4]arene and Porphyrin Tethering Four Chiral Five-Membered Cyclic Carbonates

Calix[4]arene tethering four chiral five-membered cyclic carbonates 1c was synthesized by O-glycidylation of p-tert-butylcalix[4]arene 1a with (R)-glycidyl tosylate, followed by carbonation with carbon dioxide catalyzed by lithium bromide. Porphyrin tethering chiral five-membered cyclic carbonates 2c was similarly synthesized.

ChemInform Abstract: Chiral α‐Substituted Carbonyls and Alcohols from the SN2′ Displacement of Cuprates on Chiral Carbonates: An Alternative to the Alkylation of Chiral Enolates.

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.

Chiral alpha-substituted carbonyls and alcohols from the S(N)2' displacement of cuprates on chiral carbonates: An alternative to the alkylation of chiral enolates

A highly stereoselective sequence of reactions, based on the anti-selective S(N)2' addition of cuprates to allylic carbonates, transforms alkynes or alkenyl halides into carbonyls having alpha-chiral centers. The method, which uses menthone as a chiral auxiliary, is a useful alternative to the alkylation of chiral enolates with the added advantage of allowing for the "alkylation" of sec- and tert-alkyl and aryl groups.

Enantiospecific and regioselective rhodium-catalyzed allylic alkylation: diastereoselective approach to quaternary carbon stereogenic centers.

The enantiospecific and regioselective rhodium-catalyzed allylic alkylation of a series of chiral nonracemic allylic carbonates, followed by ozonolysis and reductive lactonization, provides a convenient route to optically active gamma-lactones. Sequential alkylation and reductive alkylation furnished the alpha-quaternary-beta-ternary substituted gamma-lactone derivative as a >/=10:1 mixture of diastereoisomers.

Efficient syntheses of optically active 2-arylalkanoic acids

A highly enantioselective synthesis of 2-arylpropanoic acid was achieved, using a new developed methodology of cuprate addition to chiral carbonates derived from menthone.

Palladium‐Catalysed Intramolecular Cyclisations of Olefinic Propargylic Carbonates and application to the diastereoselective synthesis of enantiomerically pure (−)‐α‐thujone

AbstractIntramolecular [Pd2(dba)3]/tri(2‐furyl)phosphine‐catalysed (dba = dibenzylideneacetone, PhCHCHCOCHCHPh) cyclisations of olefinic propargylic carbonates I provided alk‐1‐enyl‐(3‐aza)bicyclo[3.1.0]‐hexanes VIII in good yields. A palladium cascade sequence I → II → III → IV → VII → VIII is proposed. Furthermore, chiral propargylic carbonates such as 23, 24 and 25 allowed diastereoselective formation of bicyclo[3.1.0]hexanes 29, 30 and 31, respectively. The first diastereoselective synthesis of the monoterpene, (−)‐α‐thujone 40 illustrates the potential of the method.

ChemInform Abstract: Ru‐Catalyzed Hydrogenolysis of Chiral Allylic and Propargylic Cyclic Carbonates: Synthesis of Optically Active (E)‐Allylic and Allenic Alcohols.

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.

Ru-Catalyzed Hydrogenolysis of Chiral Allylic and Propargylic Cyclic Carbonates: Synthesis of Optically Active (E)-Allylic and Allenic Alcohols

Abstract RuH2(PPh3)4-catalyzed reductive cleavage reactions of chiral allylic cyclic carbonates with ammonium formate afforded optically active (E)-allylic alcohols with excellent regioselectivity. Alternatively, hydrogenolysis of propargylic cyclic carbonates in the presence of RuH2(PPh3)4 catalyst afforded allenic alcohols as a sole products.

Ni(II)-Catalyzed Regio- and Diastereoselective Allylation of Grignards Reagents to Chiral Allylic Cyclic Carbonates

Abstract Reaction of chiral allylic cyclic carbonates with Grignards reagent in the presence of NiCl2(dppe) as a catalyst afforded the alkylated (E)-allylic alcohols with high regio- and diastereoselectivity.

Pd(0)-Catalyzed Hydrogenolysis of Allylic and Dienylic Cyclic Carbonates: Synthesis of Optically Active Homoallylic Alcohols and Allylic Alcohols

Abstract Treatment of chiral allylic cyclic carbonates with ammonium formate in the presence of Pd(0) catalyst afforded optically active homoallylic alcohols with excellent regioselectivity. However, hydrogenolysis of dienylic cyclic carbonates in the presence of Pd(0) catalyst afforded conjugated or nonconjugated (E)-dienylic alcohols depending on Pd complexes used. Using homoallylic alcohol 3c as a chiral synthon, (R)-(+)-eldanolide, the sex pheromone of the African sugarcane stem borer, Eldana saccharina, was synthesized.

Regioselective addition of organocopper-magnesium reagents to chiral dienylic cyclic carbonates

Reaction of chiral dienylic cyclic carbonates with dialkylcopper-magnesium complex R 2CuMgX (RMgX: CuI=2: 1)BF 3·OEt 2 in THF at −78 °C for 30 min afforded γ-alkylated ( E)-allylic alcohols with excellent regioselectivity and diastereoselectivity.

ChemInform Abstract: Neutral Alkylation of Chiral Allylic Cyclic Carbonates Catalyzed by a Palladium Complex.

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.

Kinetic resolution of vinyl carbonates through a lipase-mediated synthesis of their carbonate and carbamate derivatives.

Lipase from Candida antarctica was used in the synthesis of different chiral carbonates and carbamates through the enzymic resolution of the starting racemic vinyl carbonates. A striking feature was the changeover of the enantioselectivity with regard to the one showed when vinyl carbonates were used in the resolution of alcohols and amines, thus the S enantiomer of the vinyl carbonate was resolved whereas the same enzyme was selective towards R ones when resolving alcohols and amines. In this way, compounds obtained beforehand as R carbonates were now achieved as S ones with better e.e.'s and shorter reaction times.

Highly regio-, (E)-stereo-, and diastereoselective SN2′ addition of organocuprates to chiral allylic cyclic carbonates

Abstract Reaction of the cyclic carbonates of acyclic vinyl diols with RCu(CN)Li· BF 3 , RCu(CN)MgBr·BF 3 , or RMgBr·CuI (cat) in THF at −78 °C proceeded in S N 2′ fashion and resulted in the formation of alkylated ( E )-allylic alcohols with remarkably high diastereoselectivity. This reaction represents an efficient 1, 3-chirality transfer method.

Neutral alkylation of chiral allylic cyclic carbonates catalyzed by palladium complex

The cyclic carbonates of acyclic vinyl diols react with nucleophiles in the presence of a palladium complex as a catalyst under neutral conditions to afford alkylated ( E)-allylic alcohols with highly regio-, and diastereoselectivity. This reaction represents an efficient 1,3-chirality transfer method.

Vinyl carbonates as novel alkoxycarbonylation reagents in enzymatic synthesis of carbonates.

Carbonates could be obtained by enzymatic alkoxycarbonylation from vinyl carbonates, which are easily prepared from vinylchloroformate. The reaction was catalyzed by Candida antartica lipases, SP 435 and SP 435 A. The method could be also used for the synthesis of carbamates. When racemic alcohols were used, lipase catalyzed their resolution, and chiral carbonates were obtained with different enantiomeric excesses depending upon the structure of the alcohol.