Tetrahydrothiophene, reaction with sulfur

An interesting variant on the Darzens reaction has been reported featuring an in situ prepared sulfur ylide <07OL1745>. The reaction of an a-bromo amide with tetrahydrothiophene provides the sulfur ylide in situ. This sulfur ylide then undergoes the usual epoxidation reaction with a ketoamide to provide a spiroepoxide in excellent yield and diastereoselectivity. 

Potassium fluorosulfite can be prepared by the reaction of potassium fluoride with sulfur dioxide in an autoclave or by grinding potassium fluoride in a ball mill under an atmosphere of sulfur dioxide. The reaction can be carried out by treating potassium fluoride with a solution of sulfur dioxide in dimethyl sulfoxide or in tetramethylene sulfone (tetrahydrothiophene 1,1-dioxide, Sulfolane) without resorting to costly apparatus and with practically quantitative yields. The starting materials must, in every case, be completely anhydrous. 

Unusual electrophilic compounds containing sulfur are the S+—S+ dications S. yjjg reaction of dimethyl sulfide ditrifiate with dimethyl sulfide leads to the formation of tetramethyldisulfonium ditrifiate (101a). The same procedure starting from tetrahydrothiophene ditrifiate gives by reaction with tetrahydro thiophene the corresponding dication 101b (equation 105). 

The product 303 from disulfur dichloride and 2,3-dimethylbuta-l,3-diene rearranges spontaneously to the tetrahydrothiophene 304 (equation 159)150. The reaction of liquid sulfur dioxide with conjugated dienes 305 (e.g. butadiene, isoprene) results in cyclic sulfones which dissociate into their components on heating (equation 160)151 152. 

Fig. 29. Correlation between relative hydrogenolysis reactivity and the electron densities on sulfur. ( ) Reaction conditions 300°C, 71 atm, sulfided CoO-Mo03/A1203 (5). (1) DBT (2) benzo[fo]naphtho[2,3-4]thiophene (3) 7,8,9,10-tetrahydrobenzo[b]naphtho[2,3-rf]thio-phene (4) 5b,6,ll,lla-tetrahydrobenzo[fc]naphtho[2,3-d]thiophene. (O) Reaction conditions 450°C, 1 atm, sulfided CoO-Mo03/A1203(6). (5) Thiophene (6) tetrahydrothiophene (7) benzothiophene (8) 2,3-dihydrobenzothiophene. ( + ) Reaction conditions 360°C, 2.9 MPa, sulfided NiO-Mo03/Al203(3). (9) 1-Methyl-DBT (10) 2- or 3-methyl-DBT (11) 4-methyl-DBT (12) 4,6-dimethyl-DBT. (A) Reaction conditions 300°C, 102 atm, sulfided CoO-Mo03/ Al203(8). (13) 2,8-Dimethyl-DBT (14) 3,7-dimethyl-DBT (15) 4-methyl-DBT (16) 4,6-di-methyl-DBT. Reprinted with permission from Ref. 38, Ma et al. (1995). Copyright 1995 American Chemical Society.

Reaction Products. No mercaptan or tetrahydrothiophene intermediates were found in the products of shot reactions over either catalyst. Instead thiophene reacted by rejecting its hydrocarbon portion either as a butadiene-butene mixture (from chromia) or a butene-butane mixture without butadiene (from cobalt molybdate). In both cases, the sulfur was left on the catalyst as adsorbed H2S. No H2S peak was observed following any such reaction and subsequent experiments with H2S showed that the rate of desorption of H2S was negligible until much higher concentrations on the catalyst surface had been reached. 

Beiner et al. tested the collecting capacity of several metal compounds for some volatile sulfur substances. They noted high enrichment rates and good selectivity for silver sulfide. It was used in combination with membrane extraction, thermodesorption, and GC-MS to analyze sulfides, thiols, and tetrahydrothiophene from water samples. Detection limits down to the lower ng/1 range were achieved. The disadvantages of the method are the experimental equipment, the long analysis times, and displacement reactions between the matrix and analytes on the sorbent s surface. 

The biotin and lipoate synthases catalyze similar reactions, the insertion of sulfur into unactivated C—bonds to generate essential cofactors (Figures 8C and 8D). The substrate in the case of biotin synthase is dethiobiotin, with a single sulfur inserted into two C— FI bonds to generate the tetrahydrothiophene ring of biotin. In the case of lipoate synthase, two atoms of sulfur are inserted, one each into the C—bonds at positions 6 and 8 of octanoic acid to produce dihydrolipoate, which is typically isolated in the oxidized form shown in Figure 8D. (The actual... 

Under the reducing conditirms, thiophene and benzo[f>]thiophene are readily and smoothly converted into tetrahydrothiophene and 2,3-dihydrobenzo[b]thiophene with cOTiversion rates of 85% and 86%, respectively. However, for the 2-methylthiophene, the reaction went more slowly, and the conversion rate was only 11% under the same conditions (Table 6). Possible reasons for this are that substituents at C-2 or C-3 reduce the jt-acceptor character of the olefin and sterically hinder the f/ -(C,C)-coordinati(Mi mode as well. In addition, electron-donating alkyl groups enhance the dmior ability of the sulfur atom, thereby favoring S-coordination. 

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