Selective catalytic reagents acetylene

Alkyl and aryl sulfides RSH react with equimolecular amounts of p-toluenesulfonyl-acetylene, HC C-SC Tol, in CH3CN at 0 °C or room temperature in the absence of any catalytic reagent to give Z-adducts RS-CH=CH-S02Tol with total diastereo-selectivity. On the other hand, in the presence of 1.1 equiv. of NaH in THF, the same reaction affords the corresponding li-diastereoisomers also with total diastereoselec-tivity.211... 

The selective reduction of the a,p-acetylenic ketones such as 4.12 to a,p-ethylenic ketones is accomplished by reaction with DIBAH in THF-HMPA [TY2]. In the presence of a catalytic quantity of MeCu, the reduction is faster and the stereoselectivity is modified (Figure 4.4). Nevertheless, the stereoselectivity is never very high [TY2]. The reagent does not reduce the isolated triple bond of 4.13 (Figure 4.4). 

Oxammonium salts such as 81 are new and powerful oxidizing agents for the selective oxidation of alcohols to aldehydes or ketones. 28 Such salts can be generated catalytically from small amounts of a nitro-xide in the presence of a secondary oxidation procedure, either chemical or electrochemical,. 29 or with two equivalents of acid and 2 equivalents of a nitroxide. When 81 was mixed with acetylenic alcohol 82 in dichloromethane, aldehyde 83 was isolated in 93% yield. The reaction can be monitored as the initial yellow slurry changes to a white slurry and the presence of unreacted oxidant can be checked with starch. 3l It is not necessary to use anhydrous conditions, and it was discovered that the rate of reaction was enhanced by the presence of silica gel. This reagent is compatible for the mild oxidation of many alcohols, including aliphatic primary and secondary as well as allylic and benzylic alcohols. 

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