Biomedical subjects
Publications and source records attributed to Oleg A Rakitin.
Fused aromatic and heterocyclic 1,2,3,4,5-pentathiepins react with triphenylphosphine and alkynes bearing electron-withdrawing groups to give the corresponding 1,4-dithiins in high yields. Unsymmetrical alkynes add regioselectively to afford products in agreement with the electron distribution in a proposed reaction intermediate. A mechanism for these reactions is proposed.
[chemical reaction: see text]. Treatment of N-substituted 2,5-dimethylpyrroles 2 with an equilibrated mixture of disulfur dichloride and DABCO in chloroform at 0 degrees C gives pentathiepinopyrroles 3 in moderate yields; further reaction of 3 with the same mixture at room temperature leads, in an extensive reaction cascade, to bis(dithiolo)pyrroles 4 in high yield; 2 can be converted into 4 in a one-pot operation under unusually mild conditions.
Treatment of nucleophilic heterocycles like pyrroles and thiophenes, and their tetrahydro derivatives, with S2Cl2 and DABCO in chloroform at room temperature provides a simple one-pot synthesis of fused mono and bispentathiepins. N-Methylpyrrole and its 2-chloro and 2,5-dichloro derivatives and N-methylpyrrolidine all give the same dichloropentathiepin 1a. N-Ethyl, isopropyl and tert-butylpyrrolidine behave similarly; the isopropylpyrrolidine also gives the bispentathiepin 6which undergoes an intriguing rearrangement to the symmetrical monopentathiepin 1c. N-Methyl and ethyl indole give either 2,3-dichloro derivatives 8 or the pentathiepinoindoles 9, depending upon the reaction conditions. Thiophene and tetrahydrothiophene give the pentathiepin 10. X-Ray crystal structures are provided for the pentathiepins 1a and 1d, and possible reaction pathways are suggested for the extensive cascade reactions reported.
On heating with alkynes, the readily prepared 1,3-dithioles 3 undergo a new cycloaddition reaction and an unprecedented molecular rearrangement with loss of chlorine to give the first 7H-thieno[2,3-c]thiopyran-7-thiones 4 and 4H-thieno[3,2-c]thiopyran-4-thiones 5 whose structures were confirmed by X-ray diffraction. Unexpectedly, the different alkynes used to form 3 and to convert it into 4 and 5 were incorporated regiospecifically into the thiophene and thiopyran rings, respectively. [reaction: see text]
[reaction: see text] In a remarkable cascade reaction, triethylamine is converted into the thienopentathiepin 2a and the heptathiocane 3a by a preequilibrated solution of disulfur dichloride and DABCO in chloroform.
We report the synthesis of some new polysulfur-nitrogen heterocycles by cycloaddition reactions to readily available tricyclic condensed 1,2-dithiole-3-thiones. Thus, treatment of bis[1,2]dithiolopyrrole ketothione 1 with diacyl acetylenes gave the bis-aducts 2a-d. On the other hand, cycloaddition of bis[1,2]dithiolo[1,4]thiazine ketothione 3 with 1 equiv of acyl or diacyl acetylenes gave [1,3]dithiolylidenyl[1,2]dithiolo[1,4]thiazines 4a-f in fair to high yields. Catalysis by scandium triflate was used in the reactions that implied the less reactive dipolarophiles. Treatment of 3 with 2 equiv of DBA gave the bis-aduct 5a, and reaction of 4c with DMAD gave the mixed bis-adduct 5b. Cyclic voltammetry of selected examples showed irreversible processes that were influenced by the electrochemical activity of peripheral groups bonded to the heterocyclic system.
Treatment of nucleophilic heterocycles like pyrroles and thiophene, and their tetrahydro derivatives, with S2Cl2 and a base in chloroform at room temperature provides a simple one-pot synthesis of heterocyclic fused mono and bis pentathiepins such as 2, 3, 4, 5, 9, and 11.