A convenient method for the selective reduction of amides to amines

A variety of amides have been selectively reduced to the corresponding amines via conversion to their thioamides and treatment with triethyloxonium tetrafluoroborate followed by sodium borohydride. This procedure is compatible with isolated and conjugated double bonds, esters, intro groups, and sulfonamides.     

A convenient and efficient method for the synthesis of 2-hydroxy glycals

A convenient and efficient method for preparing 2-hydroxy glycals was developed from thioglycosides by using 1,4-dioxane-bromine complex/DMAP as an efficient promoter with good yield (61-85%). In this synthetic method, a wide range of sugar thioglycosides could be used as substrates.     

On triazoles XLII . A new convenient method for the N‐alkylation of highly insoluble cyclic amides

A simple N‐alkylation method of highly insoluble cyclic amides based on the high solubility of their easily isolable tetraalkylammonium and tetraalkylphosphonium salts was elaborated. The method has a rather wide scope, it is not influenced by the identity of the different rings attached to the 1,2,4‐triazolo[1,5‐a]‐pyrimidinone moiety of isomers 1 and 2 , nor the presence of the triazole substituents. It proceeds smoothly without any unwanted by‐products, at relatively low temperatures, and is not sensitive to moisture. The method allows an easy isolation of all possible N‐alkylated derivatives 3, 7 , and 8 . Spectral analysis of isomers 3, 7 , and 8 showed that our previous results concerning the formation of 3 type N‐alkylated derivatives as main products of the N‐alkylations as well as the tautomeric structure of the non‐alkylated isomers 1 and 2 is correct. However, it also showed that the isolation of a single N‐alkylated isomer 3 and its comparison with the corresponding non‐alkylated derivative to prove its tautomeric structure may lead to mistakes.     

A selective and convenient method for the synthesis of 2-phenylaminothiazolines

A series of 2-phenylaminothiazolines have been prepared from the corresponding N-(2-hydroxyethyl)-N'-phenylthioureas under mild reaction conditions using either thio-CDI (1,1'-thiocarbonyldiimidazole) or CDI (1,1'-carbonyldiimidazole) to promote the cyclization. This protocol provides the desired cyclization products in good yield with excellent selectivity. The scope and selectivity of this methodology are also described.     

B-bromo-9-borabicyclo[3.3.1]nonane. A convenient and selective reagent for ether cleavage

In methylene chloride solution, B-bromo-9-borabicyclo[3.3.1]nonane (BBr-9-BBN) readily cleaves, in excellent yield, a variety of ethers of representative structural types. The reagent can also be used for selective cleavage of one of the ether groups in a molecule containing more than one such group.     

A convenient new procedure for the oxidative cleavage of the bile acid and lanosterol side chains

A new method for the degradation of the side chain of lanosterol and bile acids is described. The cleavage was brought about by the action of molecular oxygen on basic solutions of the phenyl ketones (1, 7, and 15). Thus, the side chains were reduced by two C atoms, leading to the 23,24-bisnor series in appreciable yields. A method for converting the bisnor compounds to 20-ketosteroids is also described. The results obtained indicated that the nature of the degradation products was dependent upon the acidity of the α-hydrogen, the basic strength of the reaction medium and the nature of the solvent. A brief discussion of the mechanism is included.     

A convenient and selective synthesis of unsymmetrical benzoins via the cyanide ion catalyzed cleavage of benzils

The cyanide ion-catalyzed cleavage of benzils is used for the generation of various ‘masked’ acyl intermediates. The reaction of these intermediates with various aldehydes furnishes the corresponding esters of unsymmetrical benzoins in very good yields. A variety of unsymmetrical benzoin derivatives are synthesized in this way, including ferrocene derivatives. The hydrolysis of benzoin esters and their subsequent oxidation affords the corresponding unsymmetrical benzoins and benzils in high yield.     

A convenient method for the assignment of the absolute configuration to cyclic amines

We have assigned the absolute configuration to trans-2,5-dimethylpyrrolidine and trans-2,6-dimethyl-piperidine through radical chlorination in ω-1 position of optically active amines, 2 and 5, of known absolute configuration, followed by cyclization. CD curves of 1f and 4g derivatives indicate that the reaction is stereospecific. The absolute configuration of trans-2,5-dimethyl-Δ³-pyrròline has also been determined.     

A new method for the cleavage of nitrobenzyl amides and ethers

A mild and efficient o- and p-nitrobenzyl cleavage protocol was developed. o- and p-nitrobenzyl groups were easily removed from a variety of substrates using 20% aqueous NaOH in methanol at 75 °C, presumably via oxidation at the benzylic position by oxygen dissolved in the solution. These easily introducible and removable nitrobenzyl groups can serve as valuable protecting groups for the synthesis of multifunctional, complex molecules.     

A convenient method for the conversion of hindered carboxylic acids to N-methoxy-N-methyl (Weinreb) amides

The conversion of sterically hindered carboxylic acids to N-methoxy-N-methyl amides can be efficiently carried out with 1.1 equiv of methanesulfonyl chloride, 3 equiv of triethylamine, and 1.1 equiv of N-methoxy-N-methylamine. Yields for this process range from 59% to 88%. The major byproduct in these reactions, N-methoxy-N-methylmethanesulfonamide, can be removed by placing the product mixture under vacuum for 14-24 h.     

A convenient formal synthesis of (2S,3S)-3-hydroxy pipecolic acid

A convenient synthesis of (2S,3S)-3-hydroxy pipecolic acid starting from inexpensive and easily available l-(+)-tartaric acid has been described.     

A convenient, NMR-based method for the analysis of diastereomeric mixtures of pseudoephedrine amides

Amides of pseudoephedrine and ephedrine are shown to undergo highly stereospecific, invertive cyclization to form 4,5-dihydro-3,4-dimethyl-5-phenyl-1,3-oxazolium triflate derivatives in the presence of triflic anhydride-pyridine. 1H NMR spectra of the unpurified reaction products are remarkably clean, with sharp, well-defined peaks, and allow for rapid assessment of the diastereomeric purities of the starting amides. [reaction: see text].     

Photochemistry of imidazolides II. C2-C3 cleavage of carboxylic acid chains. A convenient new method for the side-chain degradation of bile acids and of lanosterol.

Irradiation of N-stearoylimidazole ( 1 ) gave hexadec-1-ene ( 4 ) in 45% yield, whereas irradiation of N-(4-methylstearoyl)imidazole ( 13 ) possessing a tertiary hydrogen atom γ to the carbonyl group led to 2-methylhexadec-1-ene ( 14 ) in 62% yield. These results are explained by a two-stage process: acyl migration, followed by Norrish Type II eliminatior. The reaction has been utilized for the side chain degradation of bile acids and of lanosterol, in which the second stage of the reaction was shown to proceed in up to 70% yield.     

Benzotriazol-1-yl diethyl phosphate. A new convenient coupling reagent for the synthesis of amides and peptides.

Benzotriazol-1-yl diethyl phosphate is found to be a new convenient coupling reagent for the synthesis of amides and practically racemization-free peptides.     

Thiourea,A convenient reagent for the reductive cleavage of olefin ozonolysis products

A convenient procedure for the preparation of aldehydes, in good to excellent yields, from suitable olefins by ozonolysis in methanol, followed by exposure of the resulting products to thiourea, is described.     

A convenient method for the synthesis of cyclic trithiocarbonates on carbohydrate scaffolds

An efficient regio- and stereoselective method for the synthesis of cyclic trithiocarbonates on carbohydrate skeleton is described. A freshly prepared solution of sodium trithiocarbonate reacts with cis-oriented epoxytriflate pentoses 7-11 to yield the corresponding cyclic trithiocarbonates 12-16. Structures of all new compounds are established through MS, ¹H and ¹³C NMR techniques.     

A novel synthesis of α-fluoroacetonitriles. Application to a convenient preparation of 2-fluoro-2-phenethylamines

α-Fluorophenylacetonitriles (3) are readily prepared by the treatment of the corresponding benzaldehyde cyanohydrin trimethylsilylethers (2) with diethylaminosulfur trifluoride (DAST). This method for the introduction of fluorine alpha to a cyano group is also applicable to the cyanohydrin trimethylsilylethers of aromatic ketones. Diborane reduction of the α-fluorophenylacetonitriles (3) yields 2-fluoro-2-phenethylamines (4).