Journal of Chemical Research

The transformations of 5-methoxy, 6-methoxy and 7-methoxy-α-tetralones are described. Studies on the synthesis of diterpenes veadeiroic acid 12, triptolide 18, sesquiterpenes biflorin 25, mansonone F 26, cacalol 39 and a potential intermediate for 11-deoxydaunomycinone 59 from 5-methoxy-α-tetralone 1 are discussed. Several intermediates for diterpenoid compounds and a total synthesis of phytoalexin orchinol 53 from 6-methoxy-α-tetralone 2 have been accomplished. 7-Methoxy-α-tetralone 3 has proved to be a suitable starting material for a simple and short synthesis of cadinene dihydrochloride 45.

Alkenes and alkynes were brominated efficiently in high yields with (bromodimethyl)sulfonium bromide in acetonitrile at room temperature. Alkenes produced the corresponding trans-dibromo compounds while alkynes (except phenylacetylene) afforded both the trans-dibromo products (major) and the tetrabromo derivatives (minor). However, phenylacetylene furnished solely the tetrabromo compound.

A novel photochromic compound, 3,3′- dimethyl-3,3′-dihydroxy-5,5′-dimethyl -2,2′-bi-1H-indanylidene-1,1′-dione (I), was synthesised and its structure was determined by X-ray crystallography. The compound exhibited reversible photochromism, and a stable organic radical was generated which was detected by electron spin resonance spectroscopy.

The preparation of 2-cyclohexyl-5-formyl-6-(4-bromophenyl)imidazo[2,1-b][1,3,4]thiadiazole (3) is described and its crystal structure is determined and discussed.

A one-pot multi-component reaction of phenacylbromide, thiosemicarbazide and acetyl acetone or ethyl acetoacetate is described for the preparation of the title compounds. The key features of this methodology are its operational simplicity, mild reaction conditions, and good yields.

Polarised olfinic systems are synthesised from the reaction between alkyl or aryl isocyanides and cyclic 1, 3-dicarbonyl compounds such as thiobarbituric acid, 5,5-dimethylcyclohexane-1,3-dione and cyclopentane-1,3-dione in good yield.

CuPy₂Cl₂-catalysed Mannich reaction of aromatic aldehyde, aromatic amine, and acetophenone proceeded smoothly in water to afford the corresponding β-amino carbonyl compounds in excellent yields.

One novel alkaloid, named as caldaphnidine G (1), and two known alkaloid calycicine A (2), daphnezomine L (3) were isolated from the seeds of Daphniphyllum calycinum. The structure of 1 was established by spectral methods, especially 2D NMR techniques.

One-pot syntheses of various tetrahydroquinoline-5-thiones are reported. The antimicrobial activity of the obtained products against various types of bacteria was estimated.

Zn-induced allylation of chromone-3-carbaldehyde 1 produces 3-(1-hydroxy-3-butene-1-yl)chromone 2, which gives back 1 on treatment with formalin under acidic conditions, and reacts differently towards nitrogenous nucleophiles.

23 1,6-Dihydro-1,2,4,5-tetrazine derivatives 2a-n, 3a-f, 4a-c have been synthesised by reaction of 3-(substituted phenyl)-6-methyl-1,6-dihydro-1,2,4,5-tetrazines (1a-c) with aryl isocyanates chloroformates and acyl chlorides, respectively. The yields were in the range 42-97%. It was found that a base promotes the reactions, and electron-withdrawing substituents in the benzene ring at C3 were beneficial to the yield. On substitution of the N(1) atom the conformation of the products at C(6) was inverted.

A new strategy for solid-phase synthesis of 4,5-disubstituted 2,4-dihydro-3H-1,2,4-triazol-3-ones has been developed. The 4-substituted 5-(4-hydroxyphenyl)-1,2,4-triazol-3-one derivatives were synthesised from resin-bound acylhydrazines in several steps, in good overall yields and purity.

A fast and convenient coupling reaction of terminal alkynes was achieved using (diacetoxyiodo)benzene as an oxidant in the absence of palladium catalysts, providing a simple method for the synthesis of diynes in good yields in short time.

SbCl₃ supported on montmorillonite K-10 is an efficient catalyst for the ring opening of epoxides with aromatic amines under solvent-free conditions and microwave irradiation to give the corresponding β-amino alcohols in high yields with high regioselectivity

The one-pot reaction of alkylisocyanides 1 and acetylenic esters 2 in the presence of 1, 3-diketones 3 provides an efficient access to 2-amino-4H-pyrans 4a–l. Ketenimines 5 were detected in the early stage of reaction as intermediates. The products 4a–l are stabilised by an intra molecular N-H…O hydrogen bonding.

Sodium selenite in dimethylsulfoxide is a highly efficient reagent for dehydrogenation reactions and can be used under both thermal as well as microwave irradiation conditions. Using this reagent benzoins have been dehydrogenated to benzils, flavanones to flavones and 2′-hydroxy chalcones have been converted into flavones by cyclodehydrogenation.

2-Allyl-3-benzylamino-2-cyclohexenones undergo iodine-methanol–promoted iodocyclisation under reflux to afford products characterised by combination of NMR (¹H and ¹³C), IR and mass spectroscopic techniques as the conjugated iodolium betaine derivatives of 2-iodomethyltetrahydroindolones. The zwitterionic nature of the products in solution and in the solid state was also confirmed by their chemical behaviour and the experimental data were corroborated by information from quantum chemical calculations.

Dipyridine cobalt chloride is a novel catalyst for the Pechmann condensation involving different phenols and ethylacetoacetate under solvent-free conditions using both conventional methods and microwave irradiation. It gives the corresponding coumarins in excellent yields with high purity. The catalyst is thermally stable, inexpensive and recyclable. A faster reaction and higher yields compared to the conventional method and no side products were identified using microwave irradiation. In this reaction, electron releasing groups on the phenol ring shown more reactivity and gave high yields than simple phenol. These products were identified by ¹H NMR, ¹³C NMR, MS, IR and elemental analysis.

A general protocol for the synthesis of 5-(substituted amino)-1,2,4-thiadiazoles by the cyclocondensation reaction of amidoximes with N-substituted thioureas in the presence of KF/Al₂O₃, and of 5-(cyclohexylamino)-1,2,4-oxadiazoles with DCC in the presence of KF/Al₂O₃ and thiourea, is described. The structures of the new compounds were elucidated by spectroscopic and physical data, and the crystal structure determination by X-ray diffraction of three examples.