Moderately electron-rich alkynes, such as alkynyl carboxylates 2a, b, siloxyalkynes 2c, d, an alkynyl p-toluenesulphonate 2e, and ethoxyacetylene 2f, add exclusively to the CN bond of the kinetically stabilized azete 1; with terminal alkynes 2a, f, a mixture of the regioisomeric 1-Dewar-pyridines 3 and 4 is obtained, whereas addition of internal alkynes results only in 3-oxy-1-Dewar-pyridines 3.
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Mass et al. (1990) studied this question.
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