New stereoselective entry to azaspirocyclic nucleus of halichlorine and pinnaic acids by radical translocation/cyclization reaction.

[reaction: see text] A stereoselective approach to the spirocyclic nucleus of halichlorine and pinnaic acids has been developed starting from a piperidine derivative. A key transformation in this sequence involves a cascade radical translocation/cyclization process.

Novel intramolecular [4 + 1] and [4 + 2] annulation reactions employing cascade radical cyclizations.

Tributyltin hydride and tris(trimethylsilyl)silane promote sequential/cascade free radical cyclization reactions of dienoate tethered vinyliodides or alkynes. These processes produce [4 + 1] and [4 + 2] annulated products. In contrast, the electrochemical reductions of the vinyliodides afford monocyclic compounds. Both the regiochemical and stereochemical courses of the sequential radical cyclizations strongly depend on substrate structure. Especially important is the balance between steric and stereoelectronic (Baldwin's rules) factors that serve to control cyclization regiochemistry.