Chemical Interactions of Thiosemicarbazides with 1,4‐Benzo‐ and 1,4‐Naphthoquinones

Abstract

Thiosemicarbazones 2a-e form charge-transfer (CT) complexes with chloranil (CHL), fluoranil (TFQ) and 2,3-dicyano-1,4-naphthoquinone (DCNQ). The donors 2a-d react with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) to yield 3-amino-5-arylthiadiazoles ? and DDQ-H2 (8). The thiosemicarbazide itself interacts with CHL via CT complexation to form the products 10-13. Heating of thiosemicarbazide (1) with 2,3-dichloro-1,4-naphthoquinone (DCHNQ) affords the {hiadiazine derivative 15. Recently, we have reported that the basicity of the system 2a-e stems from the conjugation between the aryl group and the x as well as n electrons and that the thiosemicarbazone system can undergo three different types of transitions based on the presence of the three donating centers X-K* (aryl group) n-x* (N atom) and n-x* (S atom)[2'].In this paper we present the results of our spectral investigation of the formation of C T complexes between the thiosemicarbazones 2a-e and several benzo-and naphthoquinones (Scheme l ) as well as of the irreversible chemical reactions observed for some donor-acceptor pairs.As shown in Table 1, the UVNIS absorption maxima obtained by mixing both donors 2a-e and the different x acceptor components in ethyl acetate as a solvent fall in the visible region. These maxima are attributed to C T complex formation, since both donor and acceptor alone d o not absorb in this region.The addition of donors 2a-e to both CHL and T F Q affords an initial C T complex, the absorbance of which does not change under the experimental conditions required for the determination of the association constants. However, on addition of 2a-e to DCNQ the initial formation of C T complexes is followed by a very slow chemical

Phenylbiguanide as electron donor in heterocyclic synthesis

“…Our long-term interest in chemical reactions induced by charge-transfer complexation forms a part of our systematic efforts to obtain new heterocyclic systems [18][19][20][21][22][23][24][25][26][27]. We have turned our attention to phenylbiguanide as electron donor towards some -acceptors, such as tetracynoethylene (TCNE), 2-dicyanomethyleneindane-1,3-dione (CNIND), 2,3-dicyano-1,4-naphthoquinone (DCNQ), tetracyanoquinodimethane (TCNQ), and 3,4,5,6-tetrachloro-1,2-benzoquinone (CHL-o), to synthesize some heterocycles with the expectation that they too might exhibit biological activity.…”

New access to pyrazole, oxa(thia)diazole and oxadiazine derivatives

“…This way of formation is not possible from precursors A, C, and D. From its IR and 13 C NMR this product does not contain a free benzoyl group any more, thus the oxadiazine structure 15 is suggested and rationalized by the sequence B → 18 → 19 → 15 (Scheme 5). …”

“…As a part of our program aimed at the development of new simple and efficient procedures for the synthesis of some important heterocyclic systems from thiosemicarbazide derivatives, we have recently reported different successful approaches for synthesis of thiazole, thiazine, thiadiazole, thiadiazine, thiadiazepine, oxathiadiazole and indazole, as SCHEME 1 well as pyridazine derivatives [12][13][14][15][16][17]. As will be outlined in detail below, in this paper we report several heterocyclizations of 4-substituted 1-benzoylthiosemicarbazides (1b-f) using ethenetetracarbonitrile ("tetracycanoethylene", 5) either as a reaction mediator or as a building block.…”

Benzo- and naphthoimidazoxadiazolediene, naphthobisthiazole as well as naphthothiazine derivatives from 1-acylthiosemicarbazides

“…Addition of nitrogen nucleophiles to benzo-and naphthoquinones represents a common synthetic route to many fused heterocyclic rings which have been used as synthetic intermediates in medicinal chemistry [3][4][5][6] and for dyestuffs [7][8][9][10][11][12][13][14][15][16] .…”

“…A series of benzo-and naphthothiazolediones have been synthesized by reaction of N-substituted thioureas with 2a, 2b and 3a 19 . Indazole, thiadiazine and naphothiadiazine derivatives were isolated from the reaction of thiosemicarbazide with 2b and 3a 10 . The reaction of N,N`-disubstituted hydrazinecarbothioamides with 2b and 3a afforded thiadiazole and thiadiazine derivatives 20 .…”