Search

3-Substituted N-Ethoxycarbonyl aziridine-2-carboxylates are opened in a regio and stereoselective fashion whether in C-2 position by NaX (X = 1, Br) or in C-3 by MgBr 2

a novel synthesis of C 1 C 10 fragment of Nystatin A 1 was accomplished: the synthetic sequence utilized, as chiral building block, a protected syn 1,3 polyol previously obtained by chemoenzymatic route. The final fully protected fragment was then transformed to a known lactone in order to demonstrate the correct relative and absolute configuration.

A short, highly efficient, stereoconvergent synthesis of the polyolic chain, C1–C13, of the macrolide antibiotic amphotericin B is described. The key features of the synthesis are the use of a single chiral precursor for the establishment of the stereogenic centres in a short synthetic sequence, and the final alkyl lithium addition to the appropriate aldehyde, which showed high diastereoselectivity for the correct stereochemistry at the fifth stereogenic centre.

α,β-Epoxy esters are opened by NaX (X = I, Br) in a regio and stereoselective fashion to β-hydroxy-α-halo esters, which represent suitable precursors of syn α-amino-β-hydroxy esters and β-hydroxy esters.

The enantio and stereoselective synthesis of (5R, 6S)-6-acetoxy-hexadecanolide is described via chemo, regio and stereoselective opening with LiI of a chiral epoxy alcohol precursor.

Differently protected glycidol derivatives (with Bn, TBDPS, TBS and MPM groups) have been tested for regioselective ring opening with vinylmagnesium bromide in order to obtain useful five-carbon functionalised homoallylic alcohols. Careful choice of the reagents and experimental conditions allowed a general access to important chiral synthons for asymmetric synthesis.

an aldol-reduction one-pot sequence allows syn-syn polyketide fragments such as 7 to be obtained enantio and diastereoselectively. Enol diisopinocampheylborinate is able to influence both the aldol and the subsequent reduction with NaBH4, via a chelate chair like intermediate.

Recent developments in the regio-, chemo- and stereoselective oxirane cleavage by new halogenating reagents allow obtention of various vicinal halohydrins. Also, epoxy alcohols and other functionalized oxiranes can be conveniently converted into the corresponding halohydrins. Some of the new methodologies have been successfully applied to the preparation of optically active fragments toward the synthesis to more complex molecules and natural products

epoxy alcohols are regio and chemoselectively opened to the corresponding iodohydrins and then reduced in situ to diols; the application of the described procedure leads to a short asymmetric of a well known pheromone. Also homoallylic (E and Z) epoxy alcohols and its benzylated derivatives shows high preference for regioselective opening affording the corresponding 1,3 diol.

several epoxides and epoxy alcohols have been opened to the corresponding halohydrins by lithium halides with Amberlyst in CH3CN at room temperature: the reaction proceeds in quantitative yields with high degree of regioselectivity.

the iterative diastereoselective reduction of a model hydroxy 3,5 diketo ester to the corresponding skipped 1,3,5 triol ester was studied in different conditions. The use of NaBH 4 /Ti(OiPr) 4 in THF leads with good stereoselection to the syn-syn triol ester as the main product; the described method has been applied to an extremely short synthesis of the C 1 –C 10 fragment (in racemic form) of the macrolide antibiotic Nystatin A 1 .

the biocatalytic desymmetrization, in presence of different enzymes, of two models of polyfunctionalized diols in a meso form was studied PFL was found to be the most selective enzyme with excellent results in chemical and optical yield with some of the tested substrates. The obtained chiral building block was utilized for some useful synthetic transformations toward the synthesis of natural products

an aldol-reduction one-pot sequence allows syn-syn polyketide fragments such as 7 to be obtained enantio and diastereoselectively. Enol diisopinocampheylborinate is able to influence both the aldol and the subsequent reduction with NaBH4, via a chelate chair like intermediate.

Recent developments in the regio-, chemo- and stereoselective oxirane cleavage by new halogenating reagents allow obtention of various vicinal halohydrins. Also, epoxy alcohols and other functionalized oxiranes can be conveniently converted into the corresponding halohydrins. Some of the new methodologies have been successfully applied to the preparation of optically active fragments toward the synthesis to more complex molecules and natural products

2,3 -epoxy alcohols-1-tosylates are regio and chemoselectively opened to the corresponding 3-halohydrins (I, Br, Cl): the reduction of the iodohydrins to the monoprotected diols and subsequent standard coupling of the tosyl group leads to a straightforward synthesis of optically active naturally occurring pheromones.

The enantio and stereoselective synthesis of (5R, 6S)-6-acetoxy-hexadecanolide is described via chemo, regio and stereoselective opening with LiI of a chiral epoxy alcohol precursor.

the first enantioselective synthesis of seiridin, a phytotoxic dialkylsubstituted butenolide produced by three Seiridium species, fungi pathogenic for cypress, is described. The short sequence, which leads to optically pure compound 1, would be useful to the obtaining of larger quantities of the compound for genetic selection of resistant cypress plants.

3-Substituted N-Ethoxycarbonyl aziridine-2-carboxylates are opened in a regio and stereoselective fashion whether in C-2 position by NaX (X = 1, Br) or in C-3 by MgBr 2

An unprecedented biocatalytic desymmetrization of a dulcitol derivative leads to optically active hexitols. The best results have been obtained with PFL or Lipase PS, with ees superior to 98% and chemical yields of 75–86%. The absolute configurations of the title chiral compounds have been determined by transformation into known bromo derivatives, already utilized for the preparation of optically active tetrahydrofurans.

Regio and stereoselective opening of three membered rings by metal halides was utilized for the enantioselective synthesis of (2 S ,3 R )-3-amino-2-hydroxydecanoic acid and (3 R )-3-aminodecanoic acid.

Chiral 3-substituted N-Boc-2,3-aziridino alcohols are opened in a regio and stereoselective fashion by MgBr 2 ; the obtained 3-bromo derivatives can be reduced and deprotected under mild conditions to the corresponding 1,2-amino alcohols.

Enzymatic desymmetrization of meso -4-methyl-3,5- syn -dioxolan-1,3,5,7-tetrol was found to be highly enantioselective leading to both acetylated enantiomers with high enantiomeric excess.

A convergent stereoselective synthesis of the (3S,5R,7R,10R,11R)-C1−C13 fragment of Nystatin A1 is reported in this paper. This fragment contains an all-syn-1,3,5-triol subunit and a syn-1,2-diol moiety. The main features of the synthesis are the enzymatic desymmetrization of a meso diol to obtain an enantiomerically pure syn-4,6-dihydroxy-2-keto-phosphonate, chiral sulfoxide chemistry to prepare an α-(R)-hydroxyaldehyde and 2-trimethylsilyl thiazole reagent to synthesize a syn-α,β-(R,S)-dihydroxy aldehyde.

The novel N-(3-benzo[b]thienyl)iminophosphoranes 1b–d react with α,β-unsaturated aldehydes and ketones 2a–e to give varying mixtures of the regioisomeric benzothieno[3,2-b]pyridines 3a–d and 4a–d as a result of preferential attack of either imino nitrogen or α-thienyl carbon at the enone carbonyl group. The findings indicate that the progressive replacement of phenyl with methyl P-substituent greatly enhances the reactivity of the phosphorane 1 and concomitantly enhances the propensity of the phosphorane itself for addition to the enone by the α-thienyl carbon.

The results obtained in the MgBr2-mediated opening of 2,3-bifunctionalized epoxides are reported. The studies showed that the chelation control of MgBr2 between different functionalities can in some cases be selective.

‘One pot’ organometallic addition and subsequent ring opening of α,β-aziridine aldehydes is reported to afford anti–syn 3-bromo-1,2-amino alcohols in high chemical yield and stereoselectivity. The sequence allows the stereoselective preparation of syn 1,2-amino alcohols.

Novel N-(2-benzo[b]thienyl)iminophosphoranes react with α,β-unsaturated aldehydes and ketones to give benzo[b]thieno[2,3-b]pyridines in an aza-Wittig/electrocyclic-ring closure process. The diphenylmethyliminophosphorane reacts with aromatic and heteroaromatic aldehydes to give iminic products: upon UV irradiation, two imines furnish cyclization products in acceptable yields.

A study on the addition of boron enolates of methyl ketones to trans α,β-epoxy aldehydes is reported. The reaction proceeds with an excellent anti stereoselectivity, consistent with the Felkin–Ahn model, toward the synthesis of hydroxylated compounds with defined stereochemistry.

2,3 epoxy alcohols ( E and Z ) underwent an unusual substitution at C-1, with the use of excess LiI at 70°, affording the corresponding 1-iodo-2,3 diols. Starting with (E) 2,3 epoxy alcohols the stereochemistry of the final diols was demonstrated to be threo ; a possible mechanism, based on some experimental data, is also showed.

several epoxides and epoxy alcohols have been opened to the corresponding halohydrins by lithium halides with Amberlyst in CH3CN at room temperature: the reaction proceeds in quantitative yields with high degree of regioselectivity.

epoxy alcohols are regio and chemoselectively opened to the corresponding iodohydrins and then reduced in situ to diols; the application of the described procedure leads to a short asymmetric of a well known pheromone. Also homoallylic (E and Z) epoxy alcohols and its benzylated derivatives shows high preference for regioselective opening affording the corresponding 1,3 diol.

Synthesis of optically active (+)-3-hydroxy-5-decanolide, (−)-massoialactone and of the recently isolated 3-hydroxy-5-icosanolide was achieved by enzyme-catalysed lactonization of racemic 3,5 dihydroxy esters with PPL in dry Et 2 O. Ees vary from 86% up to >98%.

Regio- and stereocontrolled alkoxy mercuration of α,β-unsaturated esters allows direct access to 1,3-syn diols in good yields. Demercuration of adducts leads to 1,3 skipped dihydroxy esters, alcohols, and α-halo esters. The deprotection of acetonide with Amberlyst 15 on 1,3-syn-dihydroxy esters gives the corresponding δ-lactones.