Alkoxylation-carbonylation intramolecular reactions

The most popular Pd-catalyzed method for the production of furans and benzofurans involves reactions of alkynols. Acyclic alkynols are converted into furans, while benzene substituted alkynols are transformed into benzofurans. The use of this strategy is widespread for the synthesis of benzofurans however, it is occasionally used for the syntheses of furans. For example, intramolecular alkoxylation of alkyne 189 proceeds via an alkenylpalladium complex and subsequent carbonylation to form furan 190 [156, 157]. In addition, 3 -hydroxyalkyl-benzo[/)J furans were prepared by Bishop et al. via a Pd-catalyzed heteroannulation of silyl-protected alkynols with 2-iodophenol in a fashion akin to the Larock indole synthesis [158]. In a related series of experiments, Qing demonstrated that alkynes 191 could be efficiently converted into furans 192 [159]. 

A new intramolecular addition of aminyl radicals to carbonyl groups as a method to promote a ring expansion reaction leading to lactams has been described by Kim et al. In this reaction, the aminyl radicals are generated from azides which are tethered to the a-position of cyclic ketones by a two- or three-carbon chain. The addition of this A-radical to the carbonyl group generates an alkoxyl radical which is responsible for the ring expansion reaction (Eq. 32) [21a[. 

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