Jamshed N. Lam

Heterocyclic N-Oxides and N-Imides

Heterocyclic N-oxides and N-imides show a variety of fascinating reactions. This review exemplifies their preparation, discusses their structures, and considers some of their reactions

Aminoalkylbenzotriazoles: reagents for the aminoalkylation of electron rich heterocycles

Abstract Secondary and tertiary aminoalkylbenzotriazoles react with pyrrole, indole, their N-methyl analogs and with 2-methylfuran under mild reaction conditions in the presence of a Lewis acid to afford selectively the corresponding secondary or tertiary amines.

Synthesis of new microsensor coatings and their response to test vapors : 2,4,6-trisubstituted-1,3,5-triazine derivatives

Novel 1,3,5-triazine derivatives were spray-coated onto surface acoustic wave (SAW) devices and exposed to vapors of dimethyl methylphosphonate (DMMP), chloroethyl ethyl sulfide (CEES) and water. Changes in chemiresistor and SAW responses were monitored and recorded by computer-controlled data-acquisition techniques. All the derivatives tested showed little or no chemiresistor or SAW responses to water vapor. The largest reversible chemiresistor response to DMMP vapor was observed with the dicarboxylic acid derivative. The largest SAW response to DMMP was with the dithione, and the dichloro-octylthio derivative showed the largest response to CEES.

Flash-vacuum pyrolysis of N-vinylbenzotriazoles: formation of N-phenylketenimines

A real-time analysis of the flash-vacuum pyrolysis products of 1-vinyl-, 1-(2-methylprop-1-enyl)-, and 1-styryl-benzotriazole (3), (16), and (18) has been performed by tandem mass spectrometry. In the 500–700 °C temperature range, these compounds lose nitrogen yielding the N-phenylketenimines (14), (17), and (19), respectively. At higher pyrolysis temperatures (3) gives indole (4)via isomerization of (14), whereas from (16) the secondary products of (17) are benzene and methacrylonitrile. In a preparative pyrolysis of (18) at 800 °C 2- and 3-phenylindole (9) and (10) respectively, have also been detected.

The lithiation of 1-(phenylthiomethyl)benzimidazole and related compounds

1-(Phenylthiomethyl)benzimidazole is lithiated initially at the 2-position and at low temperatures the 2-lithio derivative reacts with active electrophiles to form 2-substituted products. At higher temperatures rearrangement occurs to a rather unstable methylene-lithiated isomer, which can be trapped by weaker electrophiles. Lithiation can be directed exclusively to the methylene group by: (a) using the corresponding sulphoxide or sulphone, or (b) blocking the 2-position with a t-butyl or phenyl (not methyl) group.

The synthesis and chemistry of azolenines. Part 3. Some reactions of 4H-pyrazole quaternary salts

The preparation of some novel 4H-pyrazolium salts is described. Unlike the structurally related 2H-imidazolium salts (1), the metho-salts (2) of 4H-pyrazoles show no exchange with deuterium at the N-methyl protons. Exchange occurs readily at a 5-methyl group, anions formed at this site giving a cyanine dye (10) with triethoxymethane and benzylidene derivatives (11) and (12) with 1 mol equiv. of aromatic aldehyde. The activated benzylidene derivatives react further with an excess of aldehyde and base, apparently via an N-ylide intermediate, to give pyrazolo[5,1-b]oxazoles (15), which ring-open in the presence of acid forming N-(2-hydroxyethyl)-4H-pyrazolium salts (13). With sodium borohydride, the metho-salts (2) are reduced to 4,5-dihydropyrazoles (16), which with methyl iodide are quaternised at N-1 rather than N-2.