Addition of Heteroatomic Radicals to Acetylenic Bonds

Intramolecular Addition of Heteroatomic Radicals to Acetylenic Bonds 

for instance, may be why no cyclized products have been obtained from acetylenic iV-chloroamines under the free radical conditions discussed in Section whereas aminyl radicals easily added intramolecularly to 

In the Cy6/Cy7 case with the next homolog of 156 (R = H) no products resulting from intramolecular addition were observed, the main product identified (11%) being an isoxazole assumed to be formed in a Barton reaction in the first step.  

The homolytic cyclization of acetylenic thiols is general the best 

Of course ionic cyclization processes may be expected with acetylenic thiols, as discussed before with ethylenic thiols (Section VIII.4.A). The most extensive work has been described under basic conditions where intramolecular nucleophilic addition of the thiolate anion to the triple bond may be expected. Yields are generally similar to those obtained in homolytic cyclization but the cyclization is more regioselective, exo products such as 160 generally being the exclusive ones but exceptions are known in the Cy6/Cy7 case when heteroatoms are in the chain.  

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