Intramolecular aminolysis of trichloroethyl esters: a mild macrocyclization protocol for the preparation of cryptophycin derivatives

The bifunctional catalyst 2-hydroxypyridine (2-pyridone) is shown to promote the intramolecular aminolysis of the polyfunctionalized long-chain amino trichloroethyl ester 8 to afford cryptophycin-51 (4). This process for the construction of the macrocyclic core of cryptophycin derivatives is noteworthy for its convenience, avoidance of expensive coupling reagents, and use of mild reaction conditions.     

A versatile method for the preparation of allenic alcohols

A convenient three step procedure to a variety of allenic alcohols is described, which relies on a highly unusual partitioning between two reaction pathways depending on the mode of addition of a reagent.     

Electrochemical transacylations: A mild synthesis of esters

Esters can be synthesized by electrochemically oxidizing hydroquinone carboxylates in the presence of alcohols. High yields are obtained in acidic or basic solutions and at low temperatures.     

Enol esters: versatile substrates for Mannich-type multicomponent reactions

The interaction of cyclic enol esters with diversely substituted anilines and ethyl glyoxalate yields, under Sc(OTf)3 catalysis, disubstituted N-aryl lactams in a multicomponent reaction. The protocol allows access to the trans stereoisomers after an epimerization of the initial mixture in which the cis isomers predominate. Vinyl acetate yields quinoline derivatives, whereas isopropenyl acetate leads to the corresponding Mannich adducts.     

Triethylphosphate/Phosphorus Pentoxide as an Efficient Reagent for the Phosphorylation of Phenols

Abstract

A simple, efficient, and novel method has been developed for the phosphorylation of phenols. Treatment of phenols with a mixture of triethylphosphate/phosphorus pentoxide gives the corresponding phosphate derivatives in good yields. This method is easy, rapid, and offers good yields for the phosphorylation of phenols. The reaction of triethylphosphate with phosphorus pentoxide was also studied by variable-temperature ³¹P-NMR spectroscopy.     

Asymmetric dithioacetals II: A novel and versatile method for the preparation of chiral dithioacetals

Reaction of aldehydes with one equivalent each of a thiol and a chiral thiolacid such as (R)-(-)-α-methoxyphenylthiolacetic acid in the presence of an acidic catalyst such as ZnI₂ or p-toluenesulfonic acid yields diastereomeric mixed thioacetals in good yields which are generally readily separable. Subsequent deacylation at low temperature with sodium methoxide and alkylation of the resulting thiolate anion with a variety of electrophiles provides chiral dithioacetals with no loss of enantiomeric purity.     

Phosphorus pentasulfide and Lawesson reagent in synthesis of 1,3-thiazole-4-thiol derivatives

Available S-amidophenacylation products of thiols and sulfanylphenols on treatment with phosphorus pentasulfide or, which is better, Lawesson reagent convert into the corresponding 1,3-thiazole-4-thiol derivatives that are easily oxidized with hydrogen peroxide. The latter reaction was used to introduce a series of alkyl- or arylsulfonyl groups in the 4 position of the thiazole ring. This general approach significantly extends the limited range of synthetic procedures for 1,3-thiazole-4-thiol derivatives.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 9, 2004, pp. 1529–1533.Original Russian Text Copyright © 2004 by Belyuga, Brovarets, Drach.This revised version was published online in April 2005 with a corrected cover date.     

Novel and versatile protocol for the preparation of functionalized benzocyclotrimers

2-Bromo-3-(trimethylstannyl)cyclopenta-1,3-diene is the key-intermediate for the synthesis of vic-bromo(trimethylstannyl)bicycloolefins via Diels-Alder reaction with dienophiles. The cycloadducts can be cyclotrimerized by copper(I) 2-thiophenecarboxylate (CuTC) to afford functionalized benzocyclotrimers.     

Convenient preparation of tert-butyl esters

A general method is presented for the preparation of tert-butyl esters by the gentle warming of the carboxylic acid in the presence of excess of tert-butyl acetoacetate and a catalytic amount of acid. This method generates only low pressures, and is therefore suitable for laboratory scale pressure glassware.     

A practical method for preparation of 4-hydroxyquinolinone esters

4-Hydroxyquinolinone esters are a common motif for many medicinal agents. Several methods exist for preparation of these compounds, generally involving the use of sodium hydride, which raises significant safety issues and limits their application to large-scale synthesis. In this note a practical, safe, and general method that employs a combination of diisopropylethylamine and sodium tert-butoxide is described. This allows for the synthesis of 4-hydroxyquinolinone esters and amides in good yields.     

A versatile method for preparation of O-alkylperoxycarbonic acids: epoxidation with alkyloxycarbonylimidazoles and hydrogen peroxide

A variety of O-alkylperoxycarbonic acids ($\text{2}$) were conveniently prepared $\text{in}$$\text{situ}$ by utilizing alkyloxycarbonylimidazoles ($\text{1}$) as their precursors. Epoxidation of alkenes with such peroxy-acids was studied and their reactivities were compared with those of peroxycarboxylic acids.     

Ferric chloride: a mild and versatile reagent for the formation of 1,6-anhydro glucopyranoses

A novel method for the preparation of 1,6-anhydro glucopyranoses (mono- and disaccharides) utilizing anhydrous FeCl₃ as Lewis acid is described. Treatment of methyl 6-O-benzyl and 6-O-p-methoxybenzyl-α/β d-glucopyranosides derivatives with FeCl₃ in CH₂Cl₂ at room temperature and 40°C afforded 1,6-anhydro glucopyranosides in moderate to good yields, through a debenzylation and intramolecular glycosidation in one step. A plausible reaction pathway is proposed.     

A facile route to a versatile synthon for preparation of cis-pyrethroids

$\text{cis}$-2-Cyano-3,3-dimethylcyclopropanecarboxylic acid was obtained in >50% overall yield starting with ethyl 3,3-dimethylacrylate. The key step involved a tandem Michael reaction - intramolecular displacement to afford stereoselectively a cyclopropanoid precursor of $\text{cis}$-pyrethroids.     

A mild and efficient method for the preparation of n-tosyl amides and lactams

N-tosyl amides and lactams can be prepared easily and under mild conditions by the inter- or intramolecular condensation of carboxylic acids and secondary sulfonamides. The coupling reagent used is dicyclohexyl-carbodiimide (DCC) in the presence of 4-pyrrolidinopyridine (4-PPY) and the reactions proceed readily, usually in high yield, at room temperature.