Internal Cyclization Followed by Intermolecular Addition

Organosulfone-mediated allylation, vinylation and azidation represent very effective tin-free radical processes. However, the reported methods do not work well with primary alkyl iodides and xanthate as radical precursor, owing to in- 

Depending on the length of the tether of the sulfone used, mono and di car-bonylation products could be obtained through a multicomponent reaction. Benzenethiosulfonate thus constitutes a very efficient radical-trapping agent for acyl radicals. 

Uenoyama et al. also envisaged combining TEMPO-based radical cycUza-tions with carbonylations in order to yield precursors of the tetralone framework [131]. Surprisingly, treatment of 140 at 130 °C under a CO atmosphere directly yielded a cycUzed carboxylic acid. This was shown to arise from intermediate 141 by an unknown mechanism. The free carboxylic acid derivative could be further cycUzed into tricycUc ketone 142 using Otera s intramolecular Eriedel-Crafts procedure. 

Lee and Larock found that the characteristic tricyclic core of prostacychnes could be easily obtained by tandem radical reaction involving the trapping of a radical issued from a 5-exo-trig cyclization by an excess of stannyl enones [134]. 

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