Sulfenic acids in the carbohydrate field. Synthesis of transient glycosulfenic acids and their addition to unsaturated acceptors

A new method is described for building up anomeric glycosyl sulfoxides, via the formation of transient glycosulfenic acids and their addition to unsaturated acceptors. Thermolysis of alpha- and beta-3-[(2,3,4,6-tetra-O-acetyl-D-glucopyranosyl)sulfinyl]propanenitriles affords 1-glucosulfenic acids, which are reacted in situ with common substituted alkynes. The obtained (R(S),E)-2-[(2,3,4,6-tetra-O-acetyl-alpha-D-glucopyranosyl)sulfinyl]-2-butendioates are involved as enantiopure sulfinyl dienophiles in Diels-Alder reactions with 2,3-dimethyl-1,3-butadiene to evaluate the role that the sugar moiety plays in the steric control of the cycloaddition. This chemistry provides a direct synthetic strategy for the stereocontrolled connection between thioglycon and aglycon moieties, thus offering the basis for an easy elaboration of new molecules incorporating thiosugar residues.     

An efficient access to novel enantiomerically pure steroidal delta-amino acids

A highly chemoselective sequence of Stille and Heck couplings on the heterocyclic bromoenol triflates 2 a-c with the bicycloalkenylstannanes cis-3 and trans-3 furnished the intermediate bromobutadienes 4 a-c in good yields ranging from 73-94 %. A modified Heck coupling protocol employing the palladacycle 8 and an additional bidentate ligand such as 1,4-bis(diphenylphosphinyl)butane allowed a significant reduction in catalyst loading while still obtaining the heterocyclic 1,3,5-hexatrienes 5 a-c in good yields (71-94 %). The unsymmetrically substituted 1,3,5-hexatrienes 5 a-c in solution underwent 6pi-electrocyclizations following an optimized microwave-heating protocol to yield the steroidal tetracycles cis-7 a-c and trans-7 b (59-69 %). Tetracycles cis-7 a-c are the products of a subsequent 1,5-hydrogen shift to the thermodynamically more stable, more highly substituted diene units. Removal of the tert-butyl groups provided the novel steroidal delta-amino acid 9 a and the delta-amino acid derivatives 9 b, c in good yields (76-86 %).     

Stereospecific access to branched-chain carbohydrate synthons.

Appropriate precursors for the synthesis of D-vancosamine and L-evernitrose have been stereospecifically obtained from methyl 4,6-O-benzylidene-2-deoxy-α- and β-D-threo-hexopyranosid-3-ulose.     

Original one-pot microwave-promoted Hunsdiecker-Suzuki strategy: straightforward access to trans-1,2-diarylethenes from cinnamic acids

An original strategy combining a Hunsdiecker-type bromodecarboxylation and a Suzuki cross-coupling reaction starting from various cinnamic acids has been developed in one-pot and under microwave heating to give trans-1,2-diarylethenes in few minutes.     

Photochemical generation of radical anions. An access to novel structures

The preparation of the radical anions of tetrabenzocyclooctatetraene (TBCOT) and fluorene (FLH) by photochemical methods leads to the observation of novel structures.     

Diazo chemistry in the access to novel fatty acids linked to spiro-fused oxetane-pyrazolone scaffold

A novel free fatty acid mimetic based on the spirocyclic oxetane pyrazolone 1-oxa-6,7-diazaspiro[3.4]oct-7-en-5-one scaffold has been obtained in seven steps. The key stages are based upon the toolbox of diazo chemistry, including the F SAFE diazo transfer and Rh^II-catalyzed O–H insertion followed by base-triggered oxetane closing.     

Microwave-assisted aza-Prins reaction. Part 2: straightforward access to 2,6-disubstituted 1-azaadamantanes

Novel symmetrically and unsymmetrically disubstituted 1-azaadamantanes were prepared as a single, chiral diastereomer via double microwave-assisted aza-Prins cyclization in one-pot or sequential reaction format.     

First selective lithiation of pyridylpiperazines: straightforward access to potent pharmacophores

The three isomers of pyridylpiperazines have been lithiated for the first time. The use of a superbase, an aminoalkoxide containing lithiating agent overcomes the chelating influence of the basic piperazine nitrogens, so that selective mono lithiation occurred alpha to pyridine nitrogen. This methodology offers a new access to diverse potent pharmacophores not easily prepared by other routes.     

A novel straightforward synthesis of enantiopure tetrahydroisoquinoline alkaloids.

A novel, direct,and high-yielding stereoselective method for enantiopure 1-substituted tetrahydroisoquinolines (THIQ) is described. The successful approach, which creates the stereocenter during the formation of the THIQ nucleus is based on (i) formation of chiral 2,3-substituted perhydro-1,3-benzoxazines derived from (-)-8-aminomenthol, (ii) diastereoselective intramolecular ring opening of the N,O-acetal moiety by an arylmetal generated from the substituent at the nitrogen atom in the perhydrobenzoxazine ring, and (iii) removal of the chiral auxiliary appendage. The starting perhydrobenzoxazines are easily prepared from (-)-8-aminomenthol and two different aldehydes, and the intramolecular opening is stereospecific, leading to a single stereoisomer. The method allows the preparation of a wide variety of enantiopure 1-substituted THIQ, with different substituents at C-1, by changing the nature of the starting aldehydes.     

An example of a novel synthetic approach to alkenylpyrroles

The synthesis of 2-methyl-3-(2-propenyl)pyrrole ($\text{2}$) and E- and Z-2-methyl-3-(1-propenyl)pyrroles ($\text{3}$) via the reaction of 3-butenyl methyl ketoxime ($\text{1}$) with acetylene in the KOH-DMSO system is reported.     

Cross-coupling of highly pyramidalized alkenes: A straightforward access to functionalized tetrasecododecahedradienes

The synthesis and chemical trapping of a highly pyramidalized pentacyclo[6.4.0.0(2,10).0(3,7).0(4,9)]dodec-8-ene containing ketal functions is reported. Its cross-coupling reaction with 3, 7-dimethyltricyclo[3.3.0.0(3,7)]oct-1(5)-ene followed by a [2 + 2] retrocycloaddition reaction gives a straightforward access to functionalized tetrasecododecahedradienes.     

Aminoalkoxide-mediated formation and stabilization of phenylpyridyllithium: straightforward access to phenylpyridine derivatives

It is shown that lithium aggregates promoted the efficient metalation of phenylpyridines and stabilization of phenylpyridyllithium. The BuLi-LiDMAE superbase prevented dimerization or nucleophilic addition encountered with t-BuLi or n-BuLi. The reported selective pyridine ring lithiation of 2-, 3-, and 4-phenylpyridine alpha to nitrogen opens a straightforward access to their derivatives.     

Enantioselective straightforward access to benzo[b]thiophene analogs of Azatoxin

Horner-Wadsworth Emmons olefination followed by asymmetric hydrogenation allowed the first synthetic access to the chiral thiotryptophan with good enantiomeric excess. Oxazolidinone formation followed by a Pictet–Spengler condensation provided the benzothiophenic analog of Azatoxin.     

An efficient and straightforward access to sulfur substituted [2.2]paracyclophanes: application to stereoselective sulfenate salt alkylation

A straightforward and high-yielding access to various [2.2]paracyclophanes possessing a sulfur-based functional group is reported, the key step being a SEAr reaction mediated by a sulfonium salt. The versatility of the methodology was exemplified by an original application in sulfenate salt chemistry, from which a remarkable chirality transfer was observed.     

Simple access to novel azetidine-containing conformationally restricted amino acids by chemoselective reduction of β-lactams

Reduction with diphenylsilane and catalytic amounts of tris(triphenylphosphine)rhodium(I) carbonyl hydride resulted in an efficient, chemoselective method for the transformation of amino-acid-derived β-lactams into the corresponding azetidines, which after removal of the p-methoxybenzyl group, afforded a new family of conformationally restricted amino acids. Phe-derived compounds were obtained in enantiopure form by combining HPLC resolution of the β-lactam precursor and the above-mentioned procedure.     

An example of a novel formation of an oxepin

A novel formation of an oxepin, namely 9,10,11,12-tetrafluoro-5,6-dihydrobenzo[b]naphth[2,1-f]oxepin (5) , starting from pentafluoroacetophenone and 1-tetralone is described. Also, the same synthesis using 1-indanone affords a very different ring system namely 1,2,3,4-tetrafluoro-5,11b-dihydro-7H-benzo[c]fluoren-7-one (10) . Both synthesis undergo an intramolecular nucleophilic substitution of an ortho-fluorine. In one case, the oxygen displaces the fluorine to afford the oxepin 5 and the other a carbon is used as the nucleophile to give the polycyclic ring system 10 .     

A straightforward access to neohesperidose from naringin by acetolysis. Comparative behaviour of some flavonoid neohesperidosides and rutinosides under acetolysis

A straightforward semisynthesis of neohesperidose was performed in three-steps with 43% overall yield starting from naringin, the main flavonoid of grapefruit. In addition, the behaviour of two pairs of flavonoid 7-O-rhamnoglucosides (neohesperidosides naringin and rhoifolin; rutinosides hesperidin and diosmin) under same acetolysis conditions was compared. Results demonstrated the crucial influence of the oxidation state of the aglycone (flavanone or flavone), and of the nature of the disaccharidic moiety on the course of the reaction.     

"Clicking" on/with polymers: a rapidly expanding field for the straightforward preparation of novel macromolecular architectures

The combination of controlled polymerization techniques and "click" reactions form an efficient platform for the preparation of polymers in various architectures. In this critical review, an update of our 2007 review in Chem. Soc. Rev., we focus on the "click" reactions that have been used widely in the last four years to create new polymer architectures. Not only block copolymers and star-shaped polymers but also cyclic and dendritic macromolecules could be synthesized using these robust "click" reactions (205 references).