Phenalenannulations: Three-Point Double Annulation Reactions that Convert Benzenes into Pyrenes.

3-Point annulations, or phenalenannulations, transform a benzene ring directly into a substituted pyrene by "wrapping" two new cycles around the perimeter of the central ring at three consecutive carbon atoms. This efficient, modular, and general method for π-extension opens access to non-symmetric pyrenes and their expanded analogues. Potentially, this approach can convert any aromatic ring bearing a -CH Br or a -CHO group into a pyrene moiety.

Negative Charge as a Lens for Concentrating Antiaromaticity: Using a Pentagonal "Defect" and Helicene Strain for Cyclizations.

Incorporation of a five-membered ring into a helicene framework disrupts aromatic conjugation and provides a site for selective deprotonation. The deprotonation creates an anionic cyclopentadienyl unit, switches on conjugation, leads to a >200 nm red-shift in the absorbance spectrum and injects a charge into a helical conjugated π-system without injecting a spin. Structural consequences of deprotonation were revealed via analysis of a monoanionic helicene co-crystallized with {K (18-crown-6)(THF)} and {Cs (18-crown-6) }.

Alkynes as Synthetic Equivalents of Ketones and Aldehydes: A Hidden Entry into Carbonyl Chemistry.

The high energy packed in alkyne functional group makes alkyne reactions highly thermodynamically favorable and generally irreversible. Furthermore, the presence of two orthogonal π-bonds that can be manipulated separately enables flexible synthetic cascades stemming from alkynes. Behind these "obvious" traits, there are other more subtle, often concealed aspects of this functional group's appeal.

Copper-Catalyzed Three-Component Annulations of Alkenes, Nitrosoarenes, and N-Hydroxyallylamines To Form Fused Oxazinane/Isoxazolidine Heterocycles.

One-pot cascade annulations among nitrosoarenes, alkenes, and N-hydroxyallylamines have been achieved with CuCl/O catalysts, forming fused oxazinane/isoxazolidine heterocycles with excellent diastereoselectivity (d.r. >20:1).

Cu-catalyzed oxidative Povarov reactions between N-alkyl N-methylanilines and saturated oxa- and thiacycles.

Cu-catalyzed oxidative Povarov reactions between N,N-dialkylanilines and saturated oxa- or thiacycles with tert-butyl hydroperoxide (TBHP) are described; notably, the reactions use neither [4π] nor [2π]-motifs as the initial reagents. The use of cheap alkane-based substances as building units is of mechanistic and practical interest as two inert sp(3) C-H bonds are activated.

Copper-catalyzed aerobic oxidations of 3-N-hydoxyaminoprop-1-ynes to form 3-substituted 3-amino-2-en-1-ones: oxidative Mannich reactions with a skeletal rearrangement.

Cu-catalyzed aerobic oxidations of readily available 3-N-hydroxyaminopro-1-ynes with water, alcohols, or thiols to form diverse 3-substituted 3-amino-2-en-1-ones are described. The utility of this catalysis is manifested by a wide scope of applicable N-hydroxyl propargylamines and nucleophiles, thus enabling the design of one-pot cascade or two-step sequential reactions. Besides synthetic significances, such oxidative Mannich reactions are mechanistically interesting because structurally reorganized products were obtained.

Gold-catalyzed annulations of allenes with N-hydroxyanilines to form indole derivatives with benzaldehyde as a promoter.

Gold-catalyzed syntheses of 2,3-disubstituted indole derivatives from N-hydroxyanilines and allenes are described; these reactions require benzaldehyde as an additive to generate nitrones in situ. Our control experiments indicate that nitrones and water were indispensable in the reactions whereas N-hydroxyanilines alone were inactive nucleophiles. This synthetic method is compatible with allenes and N-hydroxyanilines with a reasonable range, further highlighting its synthetic utility.

Gold-catalyzed oxidative cyclization of 4-allenyl-1-ynes with 8-methylquinoline oxide.

Gold-catalyzed oxidative cyclizations of 4-allenyl-1-ynes with 8-methylquinoline oxide are described; diverse products are produced depending on the allenyl substituents. This reaction comprises initial formation of α-oxo gold carbenes that are attacked by allene to form allyl cation intermediates.

Regioselective synthesis of 2-(2-hydroxyaryl)pyridines from the reactions of benzynes with pyridine N-oxides.

By modifying the conditions from those in Larock's reported synthesis of 3-(2-hydroxyaryl)pyridines from benzynes, and pyridine N-oxides, we altered the regioselectivity of the reaction toward an efficient synthesis of 2-substituted pyridines. The presence of ethyl propiolate altered the regioselectivity to afford 3-substituted pyridine products instead. We conducted appropriate control experiments that enable a full understanding of the mechanism.