A gold(I)-catalyzed route to α-sulfenylated carbonyl compounds from propargylic alcohols and aryl thiols

A one-step atom efficient gold(I)-catalyzed route to α-sulfenylated ketones and aldehydes from propargylic alcohols and aryl thiols is described.     

Organocatalytic oxy-Michael addition of alcohols to α,β-unsaturated aldehydes

1,4-Addition of alcohols to α,β-unsaturated aldehydes was found to be efficiently promoted by biphenyldiamine-based catalyst 3 without formation of the acetals.     

A novel synthesis of epoxides and allylic alcohols from carbonyl compounds through α, β-epoxy sulfoxides

Treatment of α,β-epoxy sulfoxides, easily prepared from carbonyl compounds with 1 equivalent of n-butyllithium at −100 °C gave the desulfinated epoxides in good yields. The similar α,β-epoxy sulfoxides having arylmethyl group at α-position, on treatment with excess n-butyllithium at −70 °C afforded 3-aryl allylic alcohols.     

A highly stereoselective conversion of α,β-epoxy esters to α-hydroxy esters. An efficient route to optically active α-hydroxyesters

α,β-Epoxy esters were cleanly converted to α-hydroxy esters with retention of the configurations at the α-carbon atoms via MgI₂-promoted regioselective oxirane ring-opening followed by tributyltin hydride-reduction.     

Asymmetric organocatalytic oxy-Michael addition of alcohols to α,β-unsaturated aldehydes

A 1,4-addition of alcohols to α,β-unsaturated aldehydes was found to be efficiently promoted by biphenyldiamine-based catalyst 3 without formation of the acetals. An asymmetric variant of this reaction has also been performed by designing a novel axially chiral organocatalyst (R)-10c.     

A new route to heterocyclic α-dehydro α-amino esters

Heterocyclic α-dehydro α -amino esters are obtained by the reaction of ethyl N-carbomethoxy oxamate with ω-halogened phosphorus ylids.     

A new route to α-alkyl-α-fluoromethylenebisphosphonates

A new route to α-alkyl-α-fluoromethylenebisphosphonates, 2 has been developed starting from commercially available tetraethyl fluoromethylenebisphosphonate (1), and alkyl halides using either caesium carbonate in DMF or sodium dimsyl. De-esterification of 2 provided biologically important α-alkyl-α-fluoromethylenebisphosphonic acid, 3, while alkoxide-induced carbon-phosphorus bond cleavage of 2 gave α-fluorophosphonates, 4, which are useful synthons in organic synthesis.     

A general route to α-alkyl (E)-α,β-unsaturated aldehydes

Bis(trimethylsilyl)-tert-butylaldimines 3 react with aldehydes in the presence of zinc bromide at room temperature to give, after hydrolysis, the desired α-alkyl α,β-ethylenic aldehydes in good yield and with very high E stereoselectivity. The reaction was believed to proceed via the α-silyl β-siloxyimines 4.     

Lead(IV) acetate oxidative ring-opening of 2,3-epoxy primary alcohols: a new entry to optically active α-hydroxy carbonyl compounds

The treatment of 2,3-epoxy primary alcohols with lead(IV) acetate (LTA) leads to α-acetoxy aldehydes or α-acetoxy ketones, through the nucleophilic ring-opening of an intermediate oxonium and the subsequent carbon-carbon bond cleavage. This reaction represents a new route to optically active α-hydroxy carbonyl compounds.     

A new umpolung for direct γ-regioselective nucleophilic addition of alcohols to γ-enolizable α,β-unsaturated aldehydes

A direct γ-regioselective nucleophilic addition of alcohols toward γ-enolizable α,β-unsaturated aldehydes was developed using a catalytic amount of MeSO₃H (30 mol%) and a stoichiometric amount of chloranil (1.0 equiv) as the oxidant. The addition of hexafluoroisopropanol (HFIP) was found to accelerate this cross-dehydrogenative coupling, furnishing diverse alcoholic adducts with high γ-regio- and E-stereoselectivities.     

A route to stereochemically complex tetrahydrofurans using α-sulfinyl carbanions

Condensations involving α-lithiosulfinyl carbanions provide an efficient strategy for preparation of highly substituted tetrahydrofurans.     

Palladium catalyzed ring opening of furans as a route to α,β-unsaturated aldehydes

Furans may be ring opened via pallado-catalyzed reactions leading to α,β-unsaturated aldehydes and ketones tethered to indole and isoquinoline moieties. Besides their synthetic interest, these fragmentations bring interesting elements into the discussion around the reaction mechanisms involved in palladium C-H activations of electron-rich heterocycles.     

A convenient and efficient one-pot way to synthesize α,β-epoxy ketones directly from acetophenones and arylaldehydes

A convenient and efficient one-pot way to synthesize α,β-epoxy ketones directly from ketones and aldehydes has been described. Reactions were carried out at room temperature and the corresponding α,β-epoxy ketones were isolated in moderate to excellent yields.     

The acid free asymmetric intermolecular α-alkylation of aldehydes in fluorinated alcohols

The acid free asymmetric intermolecular α-alkylation of aldehydes with alcohols has been discovered using trifluoroethanol as solvent. This unprecedented system affords the enantioenriched functionalized primary alcohols (after NaBH(4) reduction) in high yields and good to excellent enantioselectivities with wide substrate scope in the absence of any acid additive.     

Two-carbon homologation of aldehydes and ketones to α,β-unsaturated aldehydes

Phosphonate reagents were developed for the two-carbon homologation of aldehydes or ketones to unbranched- or methyl-branched α,β-unsaturated aldehydes. The phosphonate reagents, diethyl methylformyl-2-phosphonate dimethylhydrazone and diethyl ethylformyl-2-phosphonate dimethylhydrazone, contained a protected aldehyde group instead of the usual ester group. A homologation cycle entailed condensation of the reagent with the starting aldehyde, followed by removal of the dimethylhydrazone protective group with a biphasic mixture of 1 M HCl and petroleum ether. This robust two-step process worked with a variety of aldehydes and ketones. Overall isolated yields of unsaturated aldehyde products ranged from 71% to 86% after the condensation and deprotection steps.     

A convenient route to azetidine-2,3-diones and cis-3β-amido azetidinones

The synthesis of 3β-amido azetidinones, 8a and 8b, via azetidine-2,3-diones is described.     

One-pot synthesis of α,β-epoxy ketones by palladium-catalyzed epoxidation-oxidation of terminal allylic alcohols

Described herein is a one-pot synthesis of α,β-epoxy ketones using a palladium-catalyzed epoxidation-oxidation sequence. Functionalized terminal allylic alcohols are treated with m-CPBA under mild reaction conditions to obtain the α,β-epoxy ketones. The main benefit of this approach is that the epoxidation of the terminal double bond and the oxidation of the secondary alcohol occured in the same reaction under mild reactions and both electron-donating and electron-withdrawing functionalities are tolerated in the reaction sequence.     

Desilylation of α-trimethylsilylmethylene-δ-lactones. A new route to α-methylene-δ-lactones

Addition of phenylthiol to α-trimethylsilylmethylene-δ-lactones affords α-phenylthi(trimethylsilyl)methyl-δ-lactones which, on treatment with tetrabutyl-ammonium fluoride and methyl acrylate give the corresponding α-methylene-δ-lactones through a one-pot double deblocking process.     

Reactions of α-imino ketones derived from arylglyoxals with (trifluoromethyl)trimethylsilane; a new route to β-amino-α-trifluoromethyl alcohols

The reactions of α-imino ketones, derived from arylglyoxals, with (trifluoromethyl)trimethylsilane (CF₃SiMe₃) in DME solution, in the presence of catalytic amount of CsF, at room temperature, yield O-silylated β-imino alcohols in the chemoselective manner. Subsequent reduction of these products with NaBH₄ in ethanolic solution leads to the corresponding β-(N-alkyl)amino-α-trifluoromethyl alcohols in good to excellent yields. Trifluoromethylation of enantiomerically pure α-imino ketones (with Ar = Ph or p-MeOC₆H₄), bearing as a chiral auxiliary the PhCH(Me) group attached to the nitrogen atom, yields mixtures of diastereomeric products in the ratio of ca. 3:2.