1-Phenylsulfonyl-2- acetylene

Lithium dimethyl and diphenylcuprates add to (phenylsulfonyl)acetylene with complete syn-stereoselectivity leading to -olefins 121. In the case of di-n-butyl and di-s-butylcuprates, 5-20% of Z-olefins 122 are also formed (equation 96)80. 

The addition of 10-mercaptoisoborneol to (phenylsulfonyl)acetylene proceeds smoothly in the presence of morpholine as a catalyst to give the (Z)-vinyl sulfone 127 (equation 98)82. 

While (Z)-l,2-bis(phenylsulfonyl)ethylene (140) does not add to dienes such as furan, cyclopentadiene, cyclo-octatetraene, indene and )S-naphthol, ( )-l,2-bis(phenylsulfonyl)ethylene (141) is more reactive and the reaction with furan proceeds at room temperature for 2 h to give the adduct in 95% yield. The reactivity of dienophiles having sulfonyl group in the [4 -t- 2]cycloaddition is shown in equation 103 °X Due to the low reactivity of ethylene and acetylene as dienophiles, forcing conditions, such as high temperature and high pressure, are necessary for [4 -1- 2]cycloaddition. The hazards associated with handling acetylene under these conditions are well known and... 

A Diels-Alder reaction of N-(carbomethoxy)pyrrole and phenylsulfonyl 6-chloro-3-pyridyI acetylene was used similarly in a total synthesis of epibatidine, an alkaloid heralded for its high analgesic potency [536]. 

The hydroboration of acetylenes (3) with diisopinocampheylborane (IpC)2BH in THF led after refunctionalisation and transesterification to the olefins (4a, b, c) isolated in good yields. Monooxidation with mCpBA led to the sulfoxide (4d) whereas the sulfone (4e) was obtained with two equivalents of mCpBA. The same sulfone (4e) could also be obtained in an excellent overall yield by radical addition of phenylsulfonyl iodide to the pinacol ester of vinylboronic acid followed by a dehydroiodination in the presence of Et2N (87 % overall yield). The carboxylic ester (4a) could be transformed into the corresponding carboxylic acid (4f) (79 % yield) 11 which led to the acid chloride (4g) by treatment with freshly distilled thionyl chloride at 0°C (91 % yield), p-keto vinylboronates are easily accessible by oxidation of the corresponding protected allylic alcohol according to the following scheme ... 

The dithiocine tetraoxide derived from cyclocondensation of binaphthodithiol with dichloroethylene and oxidation (eq 8) is a chiral version of the bis(phenylsulfonyl)ethylenes. These compounds are useful acetylene equivalents in cycloaddition reactions (see l,2-Bis(phenylsulfonyl)ethylene). Indeed, a chiral acetylene equivalent allows the preparation of optically active hydrocarbons which would be difficult to prepare by classical methods. The dithiocine tetroxide reacts with nonsymmetric dienes to give a single crystalline diastereomeric adduct in most cases. Adducts (1) and (2) were obtained from acyclic and cyclic dienes. 

Vinyl sulfones can function as acetylene equivalents through the elimination of sulfinic acid. Reck and coworkers prepared a series of vinyl sulfones for cycloaddition reactions with azides to prepare 1,2,3-triazole derivatives to be incorporated into new oxazolidinone antibacterial agents. Included in the series was the cycloaddition of l-fluoro-l-(phenylsulfonyl)ethylene with the oxizolidinone 156 to give, after elimination of phenylsulfonic acid, a 28% yield of a 1 7 mixture of the regioisomeric 4-and 5-fluorotriazoles (157 and 158) (Fig. 3.91). 

Related Reagents. l,l-Bis(phenylsulfonyl)ethylene Phenyl-sulfonylethylene a-Phenylsulfonylethyllithium 1-Phenyl-sulfonyl-2-(trimethylsilyl)acetylene ( )-l-Phenylsulfonyl-2-tri-methylsilylethylene Phenylsulfonyl(trimethylsilyl)methane. 

Radical Addition Reactions of Vinyltrimethylsilane. Reaction of the title reagent with benzenesulfonyl chloride under radical addition conditions provides ( )-l-phenylsulfonyl-2-trimethylsilylethylene (15), an acetylene equivalent in Diels-Alder reactions (eq 8). In similar fashion, thiophenol adds to vinyltrimethylsilane regioselectively.i Oxidation of the thiophe-... 

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