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The preparative method of iodonium ylides, Ph–\overset⊕I–\overset\ominusC(COR)(COR′), is improved by condensation of active methylene compounds, H2C(COR)(COR′), with iodosobenzene in the presence of acetic anhydride. Thermal and Cu-catalyzed decomposition of iodonium ylides can be differentiated and both are explained in terms of diacylcarbene intermediate with different multiplicity. For the sake of comparison diazodimedone and related compounds are also decomposed by Cu-catalysis as well as by photochemical reaction. Carbene is also found to be a highly probable intermediate. Throughout these investigations the spin multiplicity of the carbene is discussed on the basis of product distributions. Notably in the presence of homogeneous Cu-catalyst in ethanol, diazodimedone gives an insertion product to O–H bond, 2-ethoxy-3-hydroxy-5,5-dimethyl-2-cyclohexenone (XVII), whereas the iodonium ylides do not give such a compound. The formation of XVII is explained by assuming a ketocarbene-Cu-chelate complex.

Reaction of the pyridines (I) with the alkenyl or alkynyl Grignard reagents (II) in the presence of methyl chloroformate (III) yields the dihydropyridines (IV) with an α‐regioselectivity of > 98% in all cases.

ChemInform Abstract The N-(alkoxycarbonyl)pyridinium chlorides (I), formed in situ from pyridine and alkyl chloroformates, react with allyltributyltin (II) to yield the 2-substituted 1,2-dihydropyridines (III) with a high regioselectivity, along with minor amounts of the 4-substituted 1,4-dihydropyridines (IV). The same α-regioselectivity is observed in the reaction of the m-substituted pyridines (V) with methyl chloroformate (VI) and (II) as outlined in the reaction scheme. No regioselectivity is found in the reaction of (Ia) with methallyl-and crotyltributyltin (IX), producing the compounds (X) and (XI). Further reactions are describted in the original paper.

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