3. Synthetic Applications 1746 3.1. Pericyclic Reactions 1747 3.1.1. Diels−Alder Cycloadditions 1747 3.1.2. Dipolar Cycloadditions 1749 3.1.3. Ene Reactions 1750 3.1.4. Claisen Rearrangements 1750 3.2. Radical Cyclizations 1750 3.3. Transition-Metal-Catalyzed Cyclizations 1753 3.4. Ring-Closing Metathesis 1754 3.5. Electrophilic Cyclizations 1755 3.6. Other Cyclizations 1756 4. Biochemical and ...

For many years, our research group has been interested in the new developments of cobalt-mediated cyclizations. In this article, our recent achievements in the field of inter- and intramolecular [2 + 2 + 2] cyclizations are compiled.

Two new fates of imine intermediates formed on radical cyclizations of ene-sulfonamides have been identified, reduction and hydration/fragmentation. Tin hydride-mediated cyclizations of 2-halo-N-(3-methyl-N-sulfonylindole)anilines provide spiro[indoline-3,3'-indolones] or spiro-3,3'-biindolines (derived from imine reduction), depending on the indole C2 substituent. Cyclizations of 2-haloanilide...

Several new gem-disubstituent effects on cyclizations e.g., the gem-dialkoxy, -dicarboalkoxy, and -dithioalkoxy effects, have been discovered. In addition we have also observed a new vicinal disubstituent effect. A novel ring size effect of ketals on radical cyclizations has been investigated.

A new and efficient preparation of pharmacologically and biologically important 2,5-disubstituted 6-azaindoles was achieved from cyclizations of aziridin-2-yl dipropargylic alcohols as adducts of two propargyl groups to ethyl 1-benzylaziridine-2-carboxylate. The sequential cyclizations include pyrrole formation and a novel base-catalyzed intramolecular acetylenic Schmidt reaction.

The preparation of fairly strained carbocyclic ring systems by intramolecular 5-exo-trig ring closure has been well documented, and the absence of proton transfers that would compromise such cyclizations is a hallmark of this chemistry. In an effort to explore the limitations of this approach to more highly strained systems, the preparation of a stellane (tricyclo[3.3.0.0(3,7)]octane) framework...

This article reviews our contribution in the ®eld of the cobalt(I)-mediated cyclizations. The use of new unsaturated partners such as allenes extend the scope and the utility of the previously developed intramolecular [2‡2‡2] cyclotrimerization. The presence of chiral auxiliaries induced high level of diastereoselectivity in the enediynes cyclization. The discovery of cobalt(I) catalyzed ene-ty...

The chemoselective [4+2] vs. [2+2] cycloaddition between allenoates and dithioesters can be controlled by switching the nucleophilic amine catalyst. The two modes of cyclizations represent the first example of controllable and chemoselective annulations between allenoates and dienophiles catalyzed by amine. These cyclizations are useful in offering a divergent synthesis of sulfur-containing het...