Direct synthesis of diastereomerically pure glycosyl sulfonium salts

It is reported that stable glycosyl sulfonium salts can be generated via direct anomeric S-methylation of ethylthioglycosides. Mechanistically, this pathway represents the first step in the activation of thioglycosides for glycosidation; however, it can further allow for the synthesis and isolation of quasi-stable sulfonium ions, representing a new approach for studying these key intermediates.     

An efficient asymmetric synthesis of grenadamide

The cyclopropane containing natural product grenadamide has been prepared in six steps using (R)-5,5-dimethyl-oxazolidin-2-one as a chiral auxiliary for asymmetric synthesis. Key synthetic steps include the use of the β-hydroxyl group of a syn-aldol product as a ‘temporary’ stereocentre to control the facial selectivity of a directed cyclopropanation reaction, as well as the use of phenylethylamine as a nucleophile for the direct aminolysis of an N-acyl-oxazolidin-2-one intermediate.     

An efficient asymmetric synthesis of manzacidin C

A brief synthesis of manzacidin C based on a chiral silane-promoted diastereo- and enatioselective acylhydrazone-alkene [3 + 2] cycloaddition reaction has been achieved. This synthesis is the first synthesis of any of the manzacidins wherein the C(4) and C(6) stereocenters are established in a single highly stereoselective step.     

An asymmetric route to total synthesis of the furano lignan (+)-veraguensin

Total synthesis of the furano lignan (+)-veraguensin is described. The key steps involve a diastereoselective aldol-type condensation of an ester enolate having an α-chiral center with an aromatic aldehyde and a novel isomerization of the syn vicinal substituents on the furan ring via a ring opening-ring closing protocol.     

A new efficient route for multigram asymmetric synthesis of alkannin and shikonin

A short and convergent approach for the synthesis of alkannin, shikonin and shikalkin is presented. A Hauser-type annulation of cyanophthalide 26 with enone 7 affords the complete aromatic system in just one step with concomitant attachment of the entire side chain. Subsequent Corey's oxazaborolidine mediated asymmetric reduction of the above advanced intermediate, leads to the required isomer in high enantiomeric excess. Finally, a selective and high yielding deprotection protocol furnishes the title compounds as pure crystalline precipitates. Thus, a multigram synthesis of shikonin, alkannin and shikalkin is achieved in high yield and enantioselectivity.     

An efficient and versatile route to the synthesis of 9,10-dihydro-3-formylphenanthrenes

An innovative and efficient route to the synthesis of 9,10-dihydro-3-formylphenanthrenes 7 has been delineated through the ring transformation of 2-oxo-4-sec-amino-5,6-dihydro-2H-benzo[h]chromene-3-carbonitriles 4 with methyl glyoxaldimethylacetal 5 to masked 3-dimethoxymethyl-1-sec-amino-9,10-dihydrophenanthrene-3-carbonitriles 6 followed by deacetalation with Amberlyst 15 in excellent yields.     

An efficient route for the synthesis of glycosyl phosphinic acids

An efficient method for the synthesis of glycosyl phosphinic acids (21) from the corresponding C-phosphonates is described. The route developed involves three steps: reduction of the glycosyl C-phosphonate to a primary phosphine, reaction of this product with an alkylating agent to afford a secondary phosphine, and finally oxidation to the phosphinic acid. Deprotection provides compounds suitable for testing as glycosyl phosphate analogues. Although the focus of this report is the synthesis of analogues of arabinofuranosyl-containing phosphate esters, the method should be readily applicable to other systems, carbohydrate or otherwise.     

Oligomeric building block approach to the synthesis of diastereomerically pure pentathymidine 3',5'-methanephosphonates

[formula: see text] A method for a large-scale synthesis of stereodefined oligo(nucleoside 3',5'-methanephosphonates) has been developed, based on transient 3'-O protection, which allows for the conversion of the protecting chirally defined methanephosphonanilidate group, located at the 3' end of a stereoregular oligomer, into diastereomerically pure "oligomeric building blocks" for stereospecific coupling with the 5'-OH group of another oligonucleotide.     

Microwave-assisted synthesis of symmetric and asymmetric viologens

Viologens are generally synthesized by N-alkylating 4,4′-bipyridine with alkyl halides. Under conventional heating conditions, however, their synthesis suffers from long reaction times and, often, low yields. In this work, symmetric and asymmetric viologens were synthesized under the assistance of microwave irradiation in good to excellent yields and in short reaction times.     

An efficient synthesis of dexlansoprazole employing asymmetric oxidation strategy

An alternative and scalable synthesis of dexlansoprazole ((R)-(+)-1); the (R)-enantiomer of Lansoprazole with an enantiomeric excess of >99.8% is presented.     

An efficient enantioselective synthesis of florfenicol via asymmetric aziridination

An efficient enantioselective synthesis of florfenicol is accomplished in 44.7% overall yield from commercially available p-(methylsulfonyl)benzaldehyde. Key features of this synthesis are the asymmetric aziridination reaction mediated by the Wulff’s catalyst in situ derived from (R)-VANOL and diastereoselectively ring-opening of (2S,3S)-fluoroaziridine 13.     

An efficient and expeditious route to stannylallenes

(Triphenylstannyl)allenes (2) are formed in excellent yield by reacting 3-chloro-1-triphenylstannyl-1-propynes (1) with several alkylcopper(I) species RCu. An 1-alkynyl group could be introduced by using instead of RCu the zinc reagent and Pd[PPh₃]₄ as catalyst.     

An efficient and direct route to the synthesis of diaryl sulfoxides catalyzed by heteropoly acid

Heteropoly acid tungstophosphoric acid (H₃PW₁₂O₄₀) was found to be an excellent catalyst for the synthesis of symmetrical diaryl sulfoxides. The reaction was carried out in various organic solvents or ionic liquids and under solventfree condition. The reaction exhibited better results in terms of the yield and rate under solventfree condition. The catalyst was efficiently recovered from the reaction mixture and reused. The highlighting features of the present protocol are short reaction times, high yields of the products, ambient conditions, and simple workup.     

An efficient synthetic route to glycoamino acid building blocks for glycopeptide synthesis

[reaction: see text] Chemical glycopeptide synthesis requires access to gram quantities of glycosylated amino acid building blocks. Hence, the efficiency of synthesis of such building blocks is of great importance. Here, we report a fast and highly efficient synthetic route to Fmoc-protected asparaginyl glycosides from unprotected sugars in three steps with high yields. The glycosylated amino acids were successfully incorporated into target glycopeptides 7 and 8 by standard Fmoc solid-phase peptide synthesis.     

An efficient route to pentasubstituted acylferrocenes

A number of pentasubstituted acylferrocenes were selectively prepared from ferrous chloride, sodium acylcyclopentadienides, and the corresponding pentasubstituted lithium cyclopentadienides in good yields. The selectivity is governed by the different steric and electronic properties of the acylcyclopentadienides vs the pentasubstituted cyclopentadienides.     

An efficient organocatalytic route to the atorvastatin side-chain

An organocatalytic route to the synthesis of the atorvastatin side-chain, a building block present in the statin family, is described using l-proline-catalyzed α-aminooxylation of an aldehyde. The method also employs an iodine-induced intramolecular electrophilic cyclization of a carbonate to produce the iodocarbonate in a highly diastereoselective manner.