Gerrit L'abbé

Influence of electron-withdrawing N-1 substituents on the thermal behaviour of 5-azido-1,2,3-triazoles

Abstract 5-Amino-1,2,3-triazoles ( 7 ), possessing a strong electron-withdrawing N-1 substituent, cannot be converted into the corresponding azides by the diazotization method, but the diazo transfer on the conjugate bases with tosyl azide proceeds smoothly and was used in this work as a general method to obtain the azides 8 . The latter thermolyze by two different pathways, depending on the nature of the R4-substituent; i.e. rearrangement to diazoester substituted tetrazoles 12 when R4 = COOR, and decomposition to alkylidenetriazenes 16 when R4 = Ar. The diazoesters 12 can further thermolyze in benzene to norcaradienes 13 , or in nitrile solution to imidazotetrazoles 14 and 15 . The kinetics of the rearrangement 8 ⇄ 12 in different solvents at 50°C are discussed.

A fast double-stage convergent synthesis of dendritc polyethers

Two tert-butyldiphenylsilyl-protected synthons 7 and 9 are prepared in excellent yields and used in a one-pot synthesis of higher generation polyether dendrons.

Molecular rearrangements of 5-azido substituted 1,2,3-triazoles

Abstract 5-Azido-4-methoxycarbonyl-1-phenyl-1,2,3-triazole ( 8a ) and its phenyl substituted derivatives 8b , c rearrange at 60–80°C to give tetrazolyldiazoacetates 9 , which have been isolated. When the reactions are allowed to go to completion, products derived from the diazo compounds are obtained; i.e. norcaradienes ( 10 ) from benzene solutions and imidazotetrazoles ( 12 ) from nitrite solutions. The latter decompose photochemically into diazacyclopentadienonimines ( 13 ). A kinetic study of the rearrangement 8 → 9 has been carried out and the mechanism (Scheme VI) is discussed in comparison with the Dimroth rearrangement.

The oxidation of cyclic alcohols from an aqueous solution by manganese porphyrins embedded in a polydimethylsiloxane membrane

Abstract The use of [5,10,15,20-tetrakis(2,6-dichlorophenyl)porphyrinato] manganese(III) chloride [TDCPP(Mn)Cl] embedded in polydimethylsiloxane (PDMS) is reported for the oxidation of cyclic alcohols to ketones with t -butylhydroperoxide from an aqueous solution. Two important observations are made which both can be ascribed to the sorption exercised by the polymer. Firstly, compared to a homogeneous set-up much higher activities are reached with the PDMS-system. Secondly, the increase in activity is more pronounced as the ring size of the alcohol increases. The increase in TON going from a five ring to a seven ring is related to the sorption of the respective alcohols in the membrane. Thus, PDMS can be considered as a support with a threefold function. Besides immobilizing and dispersing the complexes, the carrier takes part in the reaction process by selectively sorbing the reagents. Furthermore, the catalyst retained its activity in a second run, proving the stability of this heterogeneous system. The encapsulation of metallo-porphyrins in PDMS creates a heterogeneous selective oxidation catalyst that discriminates among molecules on the basis of their mutual affinity.

Cycloaddition-elimination reactions of 4-methyl-5-phenylimino Δ2-1,2,3,4-thiatriazoline with strong electrophilic isothiocyanates. Mechanism of the isomerization process

Abstract The 3,5-bis(substituted)imino-1,2,4-dithiazolidines ( 2 ), obtained from 4-alkyl-5-arylimino-1,2,3,4-thiatriazolines and isothiocyanates, rearrange to isomeric 3,5-bis (substituted) imino-1,2,4-dithiazolidines ( 3 ) by way of a cycloaddition-elimination reaction with the isothiocyanates. The previously suggested mechanism via a Dimroth rearrangement is now disproven by cross experiments.

Synthesis and thermal rearrangement of 5-diazomethyl-1,2,3-triazoles

Abstract 5-Diazomethyl-4-methoxycarbonyltriazoles are capable of undergoing ring-degenerate rearrangements ( 19 → 20 ) when a strong electron-withdrawing substituent (e.g. p-nitrophenyl or o,p-dinitrophenyl) is located at the N-1 position. Whereas the unrearranged diazomethyltriazole 19a decomposes thermally in benzene to give the cycloheptatriene 21a , the rearranged diazo compound 20b yields the norcaradiene 22b . Several methods are described for preparing the aldehydes 11 which are the precursors of the diazomethyltriazoles.

Synthesis of thiazolo[4,3-a]isoindoles by intramolecular cycloaddition-elimination reactions of 4-methyl-5-(substituted)imino-Δ2-1,2,3,4-thiatriazolines

Abstract Fused thiazolidine 11 and thiazoline derivatives 19a–c are obtained by intramolecular cycloaddition-elimination reactions of appropriately substituted 5-iminothiatriazolines 10 and 18a–c. The incorporation of a sidechain phenyl group excercises a favorable effect on cyclization since no reaction is observed with 25. Comparable intermolecular reactions also fail to occur.

Potassium benzene-1,3,5-triyltris(ethynethiolate): a new core reagent for dendrimer synthesis

The title compound 3 is readily available from 1, 3, 5-triacetylbenzene in a three-step procedure and is an efficient trifunctional core reagent for the synthesis of dendrimers.

Spontaneous ring transformation of a 5-azido-1,2,3-thiadiazole

The reaction of 4-carbethoxy-5-chloro-1,2,3-thiadiazole (1) with sodium azide results in the formation of ethyl α-thiatriazolyldiazoacetate (3) instead of the corresponding azide (2). Two plausible mechanisms for this new rearrangement are formulated.

Synthesis of fused 1,2,4-thiadiazolines by intramolecular cycloaddition-elimination reactions of 4-methyl-5-(cyano tethered)imino-Δ2-1,2,3,4-thiatriazolines

Abstract A series of 5-imino-1,2,3,4-thiatriazolines, bearing a cyano tether at the imine function, were prepared and converted into fused 1,2,4-thiadiazole derivatives by thermolysis; these are 12a → 13, 20a → 21, 20b → 22 and 29 → 30 (Schemes 2–5). In one case, the precursor thiatriazole also underwent an intramolecular cycloaddition-elimination reaction to give a fused 1,2,4-thiadiazole; namely 17a → 18 . Thiatriazoline 33 , with an aryl group attached directly to the imine function, thermolyzed to the benzothiazole 34 .