The main modes of heterocyclic-ring synthesis in 2012 were cycloaddition, multi-component reactions, metathesis and oxidative dehydrogenation and amination reactions with copper, iron, palladium and rhodium being the most widely used transition metal catalysts. There is however a significant number of heterocycles now efficiently prepared in the absence of catalysts. Particularly noteworthy is the utilization of iodine reagents and radical oxidants as effective alternatives.
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Fawaz Aldabbagh (2013) studied this question.
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