The acid-catalysed rearrangements of 4,5-bis(2-thienylhydroxymethyl)-1,3-dithiole-2-thione

Abstract

Under strongly acidic conditions, the title compound 1 readily participates in several possible rearrangement pathways, affording a product distribution which is relative to the choice of solvent and acid catalyst. Thus, using chloroform or acetone as the solvents and HBr or HClO4 as the catalysts, compounds 2-4 have been isolated and fully characterised; in addition, compound 5 was identified in the reaction mixture and characterised by H-1 NMR spectroscopy. The reaction kinetics of the transformations have been studied by H-1 NMR spectroscopy, using deuterated chloroform or acetone as the NMR solvents. A key intermediate in the reaction mechanisms is the allylic carbocation 6, which rearranges to give the fused system 3; in the presence of bromide anions, the carbocation forms an ion-pair intermediate 7, leading to the formation of compounds 2, 4 and/or 5, depending on the solvent

Polythiophene and oligothiophene systems modified by TTF electroactive units for organic electronics

“…An efficient method for the synthesis of 25c – a compound required for synthetic pathway B – was found to be repeated sequential lithiation of vinylene trithiocarbonate ( 26 ) [ 67 ] followed by subsequent trapping of the lithium organic species with thiophenecarboxaldehyde 27 [ 60 ]. The diol 25e , formed as a product of this reaction, is unstable and undergoes various rearrangments [ 68 – 69 ] in acidic conditions. Hence, it is preferably oxidised directly to the more stable diketone 25c without delay.…”

A novel route towards formylated 1,3-dithiole-2-thiones via an unprecedented allylic 1,4-diol rearrangement

“…4 During these investigations, we discovered that one of our key intermediates, 4,5-bis[hydroxy(thien-2-yl)methyl]-1,3-dithiole-2-thione 1, rearranges under acidic conditions to give a variety of products (e.g 2), depending on the choice of solvent and acid. 5 En route to a series of dihydrofuran derivatives, we have discovered that electron-rich benzyl analogues undergo a different type of rearrangement to 1, involving an unexpected 1,4-aryl shift and the concomitant formation of an aldehyde functionality. Herein, we discuss the likely mechanism involved in the reaction sequence and comment on substituent effects.…”

Redox-active tetrathiafulvalene and dithiolene compounds derived from allylic 1,4-diol rearrangement products of disubstituted 1,3-dithiole derivatives

“…Under these conditions the diol undergoes an intramolecular rearrangement to form the ring-fused product 3 in good yield [6]. …”

“…The rearrangement products from 2 were all obtained as the major product (by tlc). By contrast, when 2 was treated with HBr in CH 2 Cl 2 , compound 7 was isolated as a yellow oil via the initially produced dihydrofuran 4 along with compound 8 (observed only by 1 H NMR) [ 6 ].…”

“…The behaviour of 4,5-bis(2-thienylhydroxymethyl)-1,3-dithiole-2-thione in the presence of perchloric acid is of particular interest. Under these conditions the diol undergoes an intramolecular rearrangement to form the ring-fused product 3 in good yield [ 6 ].…”