Indium(III) Catalyzed Reactions of Vinyl Azides and Indoles.

Indium trichloride catalyzes the reaction of vinyl azides with unfunctionalized indoles to give vinyl indoles. This is the first example of displacement of the azide group by a carbon nucleophile while preserving the vinyl function. The protocol employs very mild reaction conditions and offers excellent yields of diverse 3-vinyl indoles. It is amenable to gram scale. Access to a library of 3,3'-bis(indolyl)methanes through condensation of vinyl azides with 2 equiv of an indole is demonstrated.

Azido-Enolonium Species in C-C and C-N Bond-Forming Coupling Reactions.

Vinyl azides react with boron trifluoride activated Koser's hypervalent iodine reagent to afford azido-enolonium species. These previously unknown azido-enolonium species react efficiently with aromatic compounds, allyltrimethylsilane, and azoles under mild conditions, with no need for a transition-metal catalyst, forming C-C and C-N bonds to give a variety of α-functionalized ketones. The intermediacy of the proposed azido-enolonium species is supported by spectroscopic studies.

α-N-Heteroarylation and α-Azidation of Ketones via Enolonium Species.

Enolonium species, resulting from the umpolung of ketone enolates by Koser's hypervalent iodine reagents activated by boron trifluoride, react with a variety of nitrogen heterocycles to form α-aminated ketones. The reactions are mild and complete in 4-5 h. Additionally, α-azidation of the enolonium species takes place using trimethylsilyl azide as a convenient source of azide nucleophile.

Transition-Metal-Free Intermolecular α-Arylation of Ketones via Enolonium Species.

Herein it is shown, for the first time, that enolonium species are powerful electrophiles capable of reacting with aromatic compounds in an intermolecular manner to afford α-arylated ketones. The reaction is compatible with a variety of functional groups, is of wide scope with respect to aromatic compounds and ketone, and even works for polymerization-prone substrates such as substituted pyrroles, thiophenes, and furans. Only 1.6 to 5 equiv of the commodity aromatic substrates is needed.

Alkyne [2 + 2 + 2]-Cyclotrimerization Approach for Synthesis of 6,7-Cyclopropylallocolchicinoids.

Employing a cobalt-catalyzed [2 + 2 + 2] alkyne cyclotrimerization as the final step, the short and efficient synthesis of cyclopropylallocolchicinoid and its analogues having functional group variations at C9 and/or C10 and C11 of ring C has been accomplished.

Total Synthesis of Integrastatin B Enabled by a Benzofuran Oxidative Dearomatization Cascade.

The first total synthesis of integrastatin B, a potent HIV-1 integrase inhibitor, has been accomplished in seven steps with a 17.9% overall yield employing easily accessible starting compounds. The Oxone-mediated oxidative benzofuran dearomatization cascade has been employed as the key skeletal construct to forge the central tetracyclic nucleus.

o-Quinone Methides via Oxone-Mediated Benzofuran Oxidative Dearomatization and Their Intramolecular Cycloaddition with Carbonyl Groups: An Expeditious Construction of the Central Tetracyclic Core of Integrastatins, Epicoccolide A, and Epicocconigrone A.

The intramolecular cycloaddition of o-quinone methides (o-QMs) with a carbonyl group has been envisaged and executed successfully in the context of constructing the complex and rare [6,6,6,6]-tetracyclic core found in the integrastatins, epicoccolide A, and epicocconigrone A. These transient o-QMs were generated easily from the oxidative dearomatization of the corresponding C2-(aryl)benzofuran by employing Oxone in acetone-water at rt. The subsequent cycloaddition with the carbonyl (or conjugated olefin) present on the C2-aryl group was spontaneous.

Total synthesis of the putative structure of xylarinol†B.

The total synthesis of the putative structure of xylarinol B is described and the need to revise its structure is demonstrated. The central benzoxepine skeleton was constructed by employing a cobalt-mediated bimolecular [2+2+2] Reppe-Vollhardt alkyne cycloaddition reaction.