Cascade reactions of 4-alkenyl iodides, involving a carbonylation-cyclization-carbonylation sequence, were accomplished by a hnu/Pd system. The stereochemical outcomes suggest that radical carbonylation and subsequent acyl radical cyclization may be involved in this reaction.
[reaction: see text] Five- to seven-membered lactones were prepared from omega-hydroxyalkyl iodides and CO by atom transfer carbonylation without the need for transition metal catalysts. The reaction proceeds via a hybrid radical/ionic mechanism in which the intramolecular alcoholysis of an omega-hydroxyacyl iodide, arising from atom transfer carbonylation, leads to the lactone.
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