ABSTRACT
The reaction of beta-iodo-alpha,beta-unsaturated gamma-sultones (i.e., 4-halo-1,2-oxathiole 2,2-dioxides) in aprotic polar solvents such as DMSO or acetone, with 'soft' nucleophiles such as iodide or thioacetate, yields an allenesulfonate by a very facile halophilic ring-opening E(2)-elimination. The 'harder' nucleophile, azide ion, reacts under the same conditions to yield the corresponding beta-azido-alpha,beta-unsaturated gamma-sultone (i.e., 4-azido-1,2-oxathiole 2,2-dioxide), displacing the beta-halide by an addition-elimination mechanism. In contrast, in the hydroxylic solvent CD(3)OD at ambient temperature, various nucleophiles yield neither of the above-mentioned products, but catalyze a rapid replacement of the Calpha-H by deuterium. Factors underlying this intriguing rapid exchange are proposed. Interestingly, the beta-bromo analogue exhibits similar reactivity except for the halophilic ring-opening. Calculations indicate the relative importance of the beta-halogen and the S-O(-C) bonds in enhancing the acidity of the H-C(alpha)S(O)2- grouping.
ABSTRACT
The regiospecificity of the 1,4-addition of the recently reported novel alkoxy chlorodisulfides to 2-methyl-1,3-butadiene has been established. Allyl allenethiosulfinates formed by spontaneous [2,3]-sigmatropic rearrangement of the addition products were oxidized at 4 degrees C to the corresponding thiosulfonates. Periodate oxidation at room temperature, preferably in the presence of I2, resulted in oxidative cleavage and cyclization to beta-iodo alpha,beta-unsaturated gamma-sultines. Such sultines, with varying degrees of gamma-alkyl substitution, were also conveniently prepared by reaction of iodine with alkyl allenesulfinates.
Subject(s)
Allyl Compounds/chemical synthesis , Sulfinic Acids/chemical synthesis , Sulfonic Acids/chemical synthesis , StereoisomerismABSTRACT
[reaction: see text] In a recent article, we reported on the base-catalyzed rearrangements of dipropargyl selenides, -sulfides, -sulfoxides, and -sulfones that eventually lead to polycyclic aromatic products. In the present work, we report on the first isolation and characterization of the thiophene dioxide intermediates 5b,c from a mild tandem isomerization/cyclization/aromatization of bis(pi-conjugated propargyl) sulfones. Monoallene 2b,c and diallene 3b intermediates were also identified by NMR. A kinetic study of the rearrangement of 1a-c revealed that the unusual facile tandem process is highly dependent on the nature of gamma-substitution.
ABSTRACT
Radical (neutral) and electrophilic (cationic) ring opening reactions were studied computationally in order to probe the difference in reactivity between three and four membered rings. Using the Marcus equation we have shown that the activation energy for the four membered ring opening is close to the Marcus predicted barrier whereas three membered rings display much higher reactivity than that predicted by the Marcus equation. Thus, the reactivity of the three membered rings is enhanced, in addition to the strain release, by another factor which is not operative in the four membered rings. It is clear also that this factor is not charge dependent. The possible origin of this effect is discussed.
ABSTRACT
Sundry dipropargyloxy disulfides have been successfully prepared, and their rearrangement paths and products have been found to be dependent upon their substitution pattern. Inter alia compounds of two heretofore unknown structure types-10 and 11 on one hand and 14 and 15 on the other-have been obtained and characterized.
ABSTRACT
Substituted cinnamoyl chlorides, 11, were converted into (2-hydroxyethyl)-oxazolinium chlorides 14, N,N-bis-(2-chloroethyl)amides 16 and (2-chloroethyl)-oxazolinium chlorides 17. Although derivatives 14 which possess electron-donating substituents (Me or MeO) were more potent than those substituted by electron-withdrawing groups (NO(2), Cl or CF(3)), the difference in cytotoxic actin was not significant. Modification of the lipophilic character in a series of alkoxy-substituted derivatives 14 led to more active compounds, where 14t that possesses a 4-octyloxy-phenyl-substituent was the most potent and displayed cytotoxic activity in the microM range. It is assumed that the oxazolinium salts act as alkylating agents, and undergo nucleophilic attack on the methylene adjacent to the ring oxygen where the oxazolinium ring parallels the aziridinium ring intermediate found in classical alkylating agents.
