Catalytic generation of cesium acetylide by CsF: synthesis of 1,3-benzothiazines from cyclic sulfenamides.

An efficient synthesis of enantiopure 1,3-benzothiazines has been achieved by reaction of cyclic sulfenamides and alkylpropiolate or tosylacetylene catalyzed by cesium fluoride.

Fluoride ion and phosphines as nucleophilic catalysts: synthesis of 1,4-benzothiazepines from cyclic sulfenamides.

A new methodology, using fluoride ion as a nucleophilic catalyst, was applied for the synthesis of enantiopure 1,4-benzothiazepine from cyclic sulfenamide and electron-deficient acetylene, with high efficiency and atom economy.

A novel synthesis of 1-nosyl 3,3-dichloro-beta-lactams and derivatives.

We report herein an efficient and simple route to synthesize 1-nosyl 3,3-dichloro-beta-lactams using a Staudinger reaction between N-nosyl imines and dichloroketene. The resulting dichloroazetidines were opened to afford highly functionalized building blocks.

A stereodivergent synthesis of beta-hydroxy-alpha-methylene lactones via vinyl epoxides.

A catalytic diastereoselective sulfonium ylide epoxidation of aldehydes furnished original vinyl epoxides, having an MBH backbone. These highly functionalized building blocks were used for a formal synthesis of the antibiotic conocandin, and opened up a stereodivergent route towards beta-hydroxy-alpha-methylene lactones, core units of naturally occurring compounds. Under acidic conditions, the oxiranes were mainly transformed, with moderate to good yields, into trans beta-hydroxy-alpha-methylene lactones. On the other hand, a user-friendly palladium-catalysed CO2 insertion and cyclisation sequence gave the cis beta-hydroxy-alpha-methylene lactone counterparts along with an interesting cis-trans equilibration of the pi-allyl intermediates.

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.

Trans-(+/-)-2-tert-butyl-3-phenyloxaziridine: a unique reagent for the oxidation of thiolates into sulfenates.

Aliphatic thiolates were efficiently converted into the corresponding sulfenates by smooth oxidation with trans-(+/-)-2-tert-butyl-3-phenyloxaziridine at room temperature (five examples). Subsequent electrophilic quench with benzyl bromide led to sulfoxides (S-alkylation) in good to moderate yields. Application of the protocol to an aromatic substrate was also successful. This work represents the first valuable example of the use of this poorly active oxidizing agent in synthetic organic chemistry without the need for activating conditions.

Straightforward stereoselective synthesis of spiro-epoxyoxindoles.

[reaction: see text] The in situ preparation of a sulfonium ylide reagent achieved the highly diastereoselective epoxidation of isatins, so that a new and straightforward access to biologically significant spiro-epoxyoxindoles is provided. The first investigations of an asymmetric version are reported with enantiopure sulfides.

A straightforward asymmetric synthesis of 1,2-disubstituted ferrocenylalkyl amines with the unusual (S(Fc),S) configuration.

A useful synthesis of rare 1,2-disubstituted ferrocenylalkyl amines with (S(Fc),S) configuration has been achieved in a sequential one-pot methodology from (S)-p-tolylsulfinylferrocene.

Diastereoselective addition of enantiopure lithium tert-butylsulfinylferrocene to imines.

(S)-tert-Butylsulfinylferrocene was submitted to ortho-metalation, and the corresponding lithium derivative was trapped by alkyl or aryl imines bearing various electron-withdrawing groups on the nitrogen atom (Ts, Dpp, Boc). New aminosulfoxides were obtained with complete diastereocontrol when Dpp or Boc groups were used. The absolute configuration (SS,SFc,S) has been determined by single-crystal X-ray analysis and chemical correlation. An unusual pseudocyclic boatlike transition state has been proposed to explain the stereochemical course of this reaction.

A diastereoselective and concise synthesis of functionalised vinyl epoxides with a Morita-Baylis-Hillman backbone.

A highly diastereoselective organocatalytic synthesis of unique functionalised vinyl epoxides, displaying a Morita-Baylis-Hillman backbone, has been developed by means of an user friendly sulfonium ylide epoxidation of aldehydes from a readily available alpha-(bromomethyl)acrylamide derivative. The first result in the asymmetric version is discussed.

ortho-Metalation of enantiopure aromatic sulfoxides and stereocontrolled addition to imines.

Enantiopure aromatic (phenyl, naphthyl) and heteroaromatic (pyridyl, quinolyl, diazinyl) sulfoxides have been synthesized by reaction of (S)-tert-butyl tert-butanethiosulfinate with aryl- or heteroaryllithium derivatives. The ortho-directed metalation of the sulfoxides was performed with lithium bases. Subsequent addition of the lithiated intermediates to N-tosylimines afforded tosylaminoalkyl tert-butylsulfinyl arenes. In most cases a complete asymmetric induction was highlighted in favor of (S,S) isomers. Heating the aminosulfoxides provided an original cyclization to form novel cyclic sulfenamides. A novel enantiopure synthesis of a benzylamine was described. An application of an enantiopure aminosulfoxide as N,S ligand for the asymmetric catalysis of allylic nucleophilic substitution has been successfully tested.

Design of sulfides with a locked conformation as promoters of catalytic and asymmetric sulfonium ylide epoxidation.

[reaction: see text] A new generation of 2,5-dimethylthiolanes with a locked conformation was developed to promote the asymmetric addition of chiral sulfonium ylides to aldehydes. The novel chiral sulfur derivative 4 succeeded the synthesis of trans-stilbene oxide derivatives with enantiomeric ratios ranging from 95:5 to 98:2. This user-friendly organocatalytic process proved to be efficient with 20-10% of sulfide 4 in 1 or 2 days of reaction. An insight into the ylide intermediate conformation is given on the basis of a computational ab initio study.

Remarkably mild and simple preparation of sulfenate anions from beta-sulfinylesters: a new route to enantioenriched sulfoxides.

[reaction: see text] A general, efficient, and experimentally simple method for the generation of sulfenate salts has been developed using beta-sulfinylesters as substrates. The process is based on a retro-Michael reaction, initiated by deprotonation at low temperature. Upon treatment with alkyl halides, the liberated sulfenates are subsequently converted into sulfoxides in good to excellent yield. Extension of the methodology to an unprecedented access to nonracemic sulfoxides by introduction of an enantiopure ligand, (-)-sparteine, is also described.

Asymmetric induction of the iodolactonization reaction of alpha-sulfurated gamma-unsaturated amides.

The 1,3-asymmetric iodolactonization reaction of enantiopure alpha-sulfurated gamma-unsaturated amides has been investigated. With sulfinyl and sulfonyl groups, a poorly stereoselective reaction was observed, whereas with a sulfanyl moiety, the diastereoselectivity can be high as 96:4. The role of the oxygen atom on the sulfur moiety is discussed.

First enantioselective synthesis of vinyl oxiranes from aldehydes and ylides generated from allyl halides and chiral sulfides.

Asymmetric allylidenation of aldehydes with sulfur ylides is possible with proper substitution of the initial sulfide, to avoid the [2,3] sigmatropic rearrangement of the unsaturated ylides. One-pot reaction of (2R,5R)-dimethylthiolane with allyl halides, aldehydes, and sodium hydroxide in tert-butyl alcohol affords vinyl oxiranes in good yields. Enantiomeric excesses up to 90% and trans selectivities have been achieved with methallyl-type halides.

Highly stereoselective C-allylation of an enantiopure alpha-sulfinyl thioacetamide.

The alkylation of the lithium enolate of enantiopure alpha-cyclohexylsulfinyl thioacetamide 1 with allyl bromides 5 possessing an electron-withdrawing group at the vinylic position does not occur at the sulfur center - as expected in the sulfur series - but at the carbon center through conjugate addition followed by bromide elimination. The modest to excellent 1,2-asymmetric induction achieved by the alkylsulfinyl group (dr up to 100:0) is explained by an electronic model.

First use of axially chiral thioamides for the stereocontrol of C-C bond formation.

Several N-aryl-substituted thioamides with an axis of chirality along the N-C(aryl) bond were prepared in good to excellent yields. NMR spectra revealed preferences for the E rotamer (along the N-C(=S) bond). X-ray crystallographic analysis showed that the planes of the aryl and thioamide groups were almost perpendicular (79 degrees). For the first time, these atropisomeric thioamides were used for an asymmetric Claisen rearrangement. LDA deprotonation led selectively to the enethiolates of Z stereochemistry, and subsequent reaction with a variety of allyl halides furnished S-allyl keteneaminothioacetals. These intermediates were not detected as they rearranged readily to gamma-unsaturated thioamides in good to high yields and diastereoselectivities up to 88:12. Chemical correlation allowed the assignment of the (aR*,2R*) configuration to the major diastereoisomer. A model was proposed to explain the stereochemical course of the thio-Claisen rearrangement.