Marina Cherkinsky

A novel synthesis of isocyanates and ureas via β-elimination of haloform

Abstract A novel synthesis of isocyanates via base-induced β-elimination of haloform N-monosubstituted trihaloacetamides is described. The rate of reaction exhibits a strong dependence on the nature of the trihalomethyl group. Thus, while the reaction of tribromoacetamides proceeds at room temperature and the reaction of trichloroacetamides requires heating in polar solvents, no reaction could be observed for any of the corresponding trifluoro derivatives. This novel β-elimination of haloform from stable and readily available trihaloacetamides was applied to a “one-pot” synthesis of ureas which avoids the use of phosgene and isolation of isocyanates.

[2,3]Sigmatropic Rearrangements of Propargylic and Allenic Systems

[2,3]Sigmatropic rearrangements of propargyl sulfonium ylides along with recent advances in the correspondingsulfenate-sulfoxide and sulfinate-sulfone type rearrangements are reviewed. Some new additionalexamples of these types of transformations, including rearrangements of propargylic dialkoxy disulfidesare also surveyed.

A new approach to the synthesis of 2-vinylthiophenes and selenophenes; competition between free radical and anionic cycloaromatization of bridged di- and tetrapropargylic sulfides and selenides

A series of unknown di- and tetrapropargylic sulfides and selenides have been prepared. In the presence of t-BuOK in dry THF these compounds underwent isomerization to the corresponding diallenes, followed by a tandem anionic cyclization and aromatization to 2-vinylthiophene or selenophene derivatives. Some mechanistic studies indicated competition between free radical and anionic cycloaromatization. The latter is influenced by the nature of the bridging heteroatom, substitution of the allenyl group and base concentration.

Base-Catalyzed Reactivity of Sulfur- and Selenium-Bridged Cyclic Alkynes: Tandem Isomerization and Cycloaromatization versus Isomerization and Nucleophilic Addition

The synthesis and base-catalyzed reactivity of some novel sulfur- and selenium-bridged cyclic di- and tetralkynes, derived from 1,2- and 1,4-dihydroxybenzene and 1,2-bis(bromomethyl)benzene, are described. The cyclic propargylic sulfides and selenides undergo base-induced isomerization to the corresponding allenes, followed by cycloaromatization of the latter by diradical or anionic mechanisms, depending on the nature of the base. Because of the lack of stability of the expected diradical intermediate, the corresponding allenic sulfones undergo nucleophilic addition, which is responsible for their DNA-cleaving properties. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Rearrangements of Trihalomethyl Ketones

Abstract Trihalomethyl ketones have been prepared and their reactivity under basic conditions was investigated in terms of competition between 1,2- vs. 1,3-elimination and nucleophilic substitution. Favorskii rearrangement was the preferred process, but in those cases where electronic or steric effects were present, nucleophilic substitution became dominant. No evidence of ketene formation was detected. The mechanism of formation of the various rearrangement products is discussed.

A new synthesis of N-sulfinylamines via β-elimination of chloroform from trichloromethanesulfinamides

Abstract The synthesis of various N-monosubstituted trichloromethanesulfinamides by two alternative and novel procedures is described. All these compounds have been found to undergo base-induced elimination of chloroform with formation of the corresponding N-sulfinylamines. Reaction proceeds smoothly under mild conditions.

Preparation of trichlorothioacetamides and their unexpected rearrangement to thiooxamides

Abstract The preparation of several N-monosubstituted trichlorothioacetamides by thionation of the corresponding acetamides, with the use of Heimgartners reagent is described. In contrast to the corresponding amides which undergo base-induced β-elimination of chloroform, the title compounds undergo an unexpected rearrangement to thiooxamides. The reaction mechanism is discussed.

Synthesis and structure of novel sulfur bridged cyclic di- and tetraalkynes

Abstract Some novel sulfur bridged 13- to 30-membered cyclic di- and tetraalkynes derived from 1,2-, 1,3- and 1,4-dihydroxybenzene and 1,2-bis(bromomethyl)benzene were synthesized and their structures confirmed by X-ray analysis. The unexpected formation of 2,6-divinyl-1,4-dithiin during Na 2 S/alumina induced cyclization was also observed and the reaction mechanism is discussed.

Recent Progress on Rearrangements of Sulfones

Abstract The present review surveys the main literature reports on rearrangements of sulfones published during the last decade. The report concentrates on the three most studied rearrangements, namely, 1,3-sulfonyl migration, Ramberg-Backlund rearrangement and pinacol-reduction rearrangement. Both mechanistic aspects and synthetic applications have been emphasized. The first type of rearrangements has been found to occur by both free radical as well as ionic mechanism. A number of synthetic applications, including intramolecular rearrangement-cyclization and regioselective alkene synthesis have been described. With regard to Ramberg-Backlund rearrangement, it is of special interest to note the novel isolation of previously postulated episulfone intermediate, and the renewed interest in this type of rearrangement as well as its various important modifications. Due to the novel developments a number of synthetic applications have been described, including preparation of various natural products, novel elect...

Thermal rearrangements of bis-allenyl thiosulfonates. Synthesis of novel thienothiophene and thieno-oxathiine derivatives

The synthesis and thermal rearrangement of bis-allenyl thiosulfonates are described. Bis-γ,γ-disubstituted allenyl thiosulfonates have been prepared by disproportionation of the corresponding allenesulfinic acids. On heating, these compounds unexpectedly rearrange to a mixture of 1H,3H-thieno[3,4-d][1,2]oxathiine-3-oxide 8, 1H,3H-thieno[3,4-c]thiophene-2,2-dioxide 9, and 3-alkyl-4-alkenylthiophene 10. A tentative reaction mechanism involving sequential sigmatropic rearrangements and cyclizations is suggested.