Thiolates 1,3-cycloaddition, anionic

The formation of complexes of l,2,3,4-thiatriazole-5-thiol has been well described in CHEC-II(1996) 1,2,3,4-thiatriazole-5-thiol can form complexes with various metals such as palladium, nickel, platinum, cobalt, zinc, etc. <1996CHEC-II(4)691>. These complexes can be prepared either by cycloaddition reactions of carbon disulfide with metal complexes of azide anion (Equation 20) or directly from the sodium salt of l,2,3,4-thiatriazole-5-thiol with metal salts. For instance, the palladium-thiatriazole complex 179 can be obtained as shown in Equation (20) or it may be formed from palladium(ll) nitrate, triphenylphosphine, and sodium thiatriazolate-5-thiolate. It should be noted that complexes of azide ion react with carbon disulfide much faster than sodium azide itself. 

We shall end this section with a beautiful illustration of an intramolecular 1,3-dipolar cycloaddition of a nitrile oxide that was used in the synthesis ofthe vitamin biotin. Starting at the beginning of the synthesis will allow you to revise some reactions from earlier chapters. The starting material is a simple cyclic allylic bromide that undergoes an efficient 5 2 reaction with a sulfur nucleophile. In fact, we don t know (or care ) whether this is an 5 2 or S 2 reaction as the product of both reactions is the same. This sort of chemistry was discussed in Chapter 23 if you need to check up on it. Notice that it is the sulfur atom that does the attack—it is the soft end of the nucleophile and better at Sn2 reactions. The next step is the hydrolysis ofthe ester group to reveal the thiolate anion. 

Dithiol-2-imines, formation in 1,3-anionic cycloaddition reactions of a,/3-unsaturated thiolates 87UK267. 

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