A novel and efficient synthesis of (+)- and (−)-trans-2-aminocyclohexanol by enzymatic hydrolysis

Both enantiomers of trans-2-aminocyclohexanol were obtained by enzymatic hydrolysis of (±)-2-azidocyclohexanoates using lipases and subsequent hydrogenation.     

Enantiodivergent synthesis of (+)- and (−)-isolaurepan

The enantiodivergent synthesis of (+)-and (?)-isolaurepan was achieved from a common chiral template easily available from tri-O-acetyl-d-glucal, using as key step a diastereoselective thermal Claisen rearrangement, combined with a ring expansion reaction using trimethylsilyldiazomethane.     

Concise enantiodivergent synthesis of (+)- and (−)-trans-quercus lactones

A concise enantiodivergent total synthesis of (+)- and (−)-quercus lactones from the known tricyclic lactone (+)-1 as a single chiral template was achieved using the diastereoselective nucleophilic addition of organometallic reagents as the key step.     

The synthesis of (−)-cis- and (−)-trans-crobarbatic acid

The synthesis of both cis- and trans-crobarbatic acid is reported. The five-step sequence proceeds in high yield and with control of both relative and absolute stereochemistry. The key step in the synthesis is the Birch reductive alkylation of a chiral furoic acid which sets the absolute stereochemistry of the products. The stereochemistry of the compounds described was proven unambiguously by X-ray crystallography on one synthetic intermediate and on trans-crobarbatic acid.     

The synthesis of either (+) or (−) trans-2,5-dimethylpyrrolidine

Trans-2,5-dimethylpyrrolidine, in either optical series, is prepared starting from D or L-alanine in an efficient and reasonably brief reaction sequence.     

A simple asymmetric synthesis of (+)- and (−)-2,6-diaminopimelic acids

The asymmetric synthesis of both the enantiomers of 2,6-diaminopimelic acid (2,6-DAP) has been accomplished starting from the chiral synthon 1.     

An efficient synthesis of enantiopure (+)- and (−)-3-exo-amino-7,7-dimethoxynorbornan-2-exo-ols

We describe the synthesis of new amino alcohols (+)- and (−)-3-exo-amino-7,7-dimethoxynorbonan-2-exo-ols. The (+)- or (−)-7,7-dimethoxy-1,4,5,6-tetrachlorobicyclo[2.2.1]hept-5-en-2-endo-ol, obtained from the enzyme catalysed transesterification of the racemate, was reduced and dechlorinated (Na/NH₃; ethanol), followed by pyridinium chlorochromate oxidation of the resultant alcohols to the corresponding ketones. After treatment with t-BuOK/BuONO, in a nitrosation reaction, α-keto oximes were obtained. Reduction over two steps with NaBH₄ and NaBH₄/NiCl₂·6H₂O followed by in situ acetylation furnished the corresponding acetamido esters, which were hydrolysed with CH₃OH/Na to produce the enantiopure amino alcohols in good yields.     

First synthesis of (+)- and (−)-elvirol based on an enzymatic function

A highly enantioselective synthesis of versatile chiral synthons possessing one stereogenic center, (S)- and (R)-4-aryl-5-hydroxy-(2E)-pentenoate 3 was achieved based on the enzymatic reaction of (±)-4 with commercially available lipase ‘OF-360’ from Candida rugosa. An application of (S)-3 and (R)-3 to the total syntheses of (S)-elvirol 1 and (R)-elvirol 1, respectively, is described.     

The first regio- and diastereoselective synthesis of homochiral perhydroimidazoisoxazoles via the 1,3-dipolar cycloaddition of imidazoline 3-oxides with (1S)-(−)-β-pinene

The 1,3-dipolar cycloaddition of imidazoline 3-oxides 1 with (1S)-(−)-β-pinene proceeds regio- and diastereoselectively to give homochiral perhydroimidazoisoxazole derivatives 3 in high yields in the cases of imidazoline 3-oxides 1a–e but in low yields in the reactions of 1f–g. The preferred attack of (1S)-(−)-β-pinene to the cyclic nitrone was shown to be anti–endo. The reaction of racemic nitrones (±)-1f–g with the homochiral β-pinene gave the adduct from the (S)-nitrone and the corresponding imidazole. The adducts 3 undergo retro-1,3-dipolar cycloaddition when heated in the condensed phase or in diphenyl ether to give the corresponding imidazole and β-pinene.     

Enantioselective syntheses of (+)- and (−)-brazilin

Two enantiomers of brazilin were prepared in 9 steps from 7-hydroxychroman-4-one using the AD-mix-α and AD-mix-β-directed enantioselective dihydroxylation of 3-(4-hydroxy-3-methoxyphenyl)-2H-chromen-7-ol as a key step.     

Synthesis of (+)- and (−)-Phaselic Acid

The syntheses of both enantiomers of phaselic acid (2-O-caffeoylmalate) are described. The previously unreported acetate-protected caffeic acid anhydride was used with appropriately protected malic acid derivatives as coupling partners to provide fully protected phaselic acid. Sequential unmasking of the protecting groups afforded phaselic acid in an acceptable overall yield.

Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file.     

Enantioselective synthesis of the quinolizidine alkaloids (+)-myrtine and (−)-epimyrtine

The enantioselective synthesis of (+)-myrtine 1 and (−)-epimyrtine 2 is described starting from (S)-2-(2-hydroxypropyl)allyltrimethylsilane 4 using an intramolecular allylsilane N-acyliminium ion cyclization.     

Enzymatic resolution of (±)-cis- and (±)-trans-1-aminoindan-2-ol and (±)-cis- and (±)-trans-2-aminoindan-1-ol

Pseudomonas cepacia lipase (PSL) efficiently catalyses the kinetic resolution of (±)-cis- and (±)-trans-1-aminoindan-2-ol through the O-acylation reaction of the corresponding N-benzyloxycarbonyl derivative using vinyl acetate as the acyl donor. In a similar way, cis-N-Cbz-2-aminoindan-1-ol is resolved when isopropenyl acetate is used as the acylating agent. The enantioselectivity of the reaction was lower for (±)-trans-N-Cbz-2-aminoindan-1-ol due to the different steric requirements for the two conformers of this substrate.     

Efficient synthesis of (−)-(R)- and (+)-(S)-rolipram

A novel, efficient and protecting group free enantioselective synthetic approach of (?)-(R)-1 and (+)-(S)-rolipram 2 is described employing the organocatalyzed asymmetric Michael addition, Henry condensation, Wittig olefination and reductive lactamization reactions as key steps.     

Highly enantioselective synthesis of (+)- and (−)-perfluoroalkyl(aryl) homoallyl alcohols

Asymmetric allylboration of perfluoroaldehydes and fluorine substituted aromatic aldehydes with ^dIpc₂BAll and 2-Icr₂BAll has been investigated. Both enantiomers of the fluorinated homoallyl alcohols were obtained in high yields and excellent enantiopurity (95–99% ee).     

Total synthesis of (−) verbenalol and (−) epiverbenalol

The first asymmetric synthesis of (−) verbenalol and (−) epiverbenalol, starting from the organometallic complex (−) 1, is described.     

Diastereoselective α-iminoamine rearrangement: asymmetric synthesis of (R)-(−)- and (S)-(+)-2-benzyl-2-hydroxycyclohexanone

A convenient asymmetric synthesis of both (R)-(−)- and (S)-(+)-2-benzyl-2-hydroxycyclohexanones starting from racemic 2-benzyloxycyclohexanone and the chiral auxiliary 1-phenylethylamine is reported. The route involves a [1,3]-sigmatropic shift and a new diastereoselective α-iminoamine rearrangement of a 2-benzyl-2-iminocyclohexanamine substrate.     

A convenient synthesis of (+)-albicanol based on enzymatic function: total syntheses of (+)-albicanyl acetate, (−)-albicanyl 3,4-dihydroxycinnamate, (−)-drimenol, (−)-drimenin and (−)-ambrox

By using lipase ‘PL-266’ from Alcaligenes sp. enantioselective acetylation of (±)-albicanol 4 with isopropenyl acetate gave the enantiomerically pure (+)-albicanyl acetate 3 and (+)-albicanol 4. Deprotection of (+)-3 afforded the natural (+)-albicanol 4 which was converted to the natural products (−)-albicanyl 3,4-dihydroxycinnamate 7, (−)-drimenol 8, (−)-drimenin 9 and (−)-ambrox 10.     

Studies on the synthesis of chiral nonracemic 3,4-disubstituted azepanes,a formal synthesis of (+)- and (−)-balanol

Sugar lactones were converted to 3,4-disubstituted azepanes and caprolactam derivatives by selective deoxygenation, functionalization and reductive cyclization. The cyclization proved troublesome with 6-azidolactols but led to good results with the corresponding lactones. A formal synthesis of (+)- and (−)-balanol is reported.