Halocyclobutanol Dehydration En Route to Halocyclobutenes

A new method for the preparation of halocyclobutenes is described. The developed process involves the dehydration of halocyclobutanols by using tetrafluoroboric acid–diethyl ether complex in dichloromethane at room temperature. The process allows for high yields of halocyclobutenes to be achieved by using alcohols that do not trigger the formation of isomeric allylic halides.

Steric- and Electronic-Controlled Intramolecular [2 + 2]-Cycloaddition of Cyclohexadienone-Containing 1,7-Enynes

Herein we have developed the silver-catalyzed electronic- and steric-controlled intramolecular formal [2 + 2]-cycloaddition of alkyne-tethered cyclohexadienones. Substrates with electron-rich alkynes and a less hindered quaternary carbon center afford tricyclic fused cyclobutenes through 1,7-enyne cyclization. In contrast, the formation of dihydrofurans was observed from electron-deficient alkynes via proton abstraction/C-O bond cleavage. The synthetic potential of this method was also broadened with a gram-scale reaction and various transformations on cyclobutene.

Brønsted-acid-catalyzed one-pot tandem annulation/[5 + 2]-cycloaddition of o-propargyl alcohol benzaldehydes with alkynes: regioselective and stereoselective synthesis of dibenzo[a,f]azulen-12-ones

The one-pot synthesis of dibenzo[a,f]azulen-12-ones has been established starting from o-propargyl alcohol benzaldehydes and alkynes.

Harnessing the Polarizability of Conjugated Alkynes toward [2 + 2] Cycloaddition, Alkenylation, and Ring Expansion of Indoles

Reported is the utilization of electronically biased conjugated alkynes in the development of highly diastereo- and regioselective dearomative [2 + 2] cycloadditions, alkenylations, and ring expansions of electron-rich indoles. Regioselective protonations of cross- and linear-conjugated alkynes were found to be crucial for accessing various cyclobutene-fused indoline and alkenylated indole derivatives. Furthermore, the facile ring expansion of [2 + 2] keto adducts, which were successfully synthesized from ynones, provided 1 H-benzo[ b]azepine scaffolds.

Catalytic Double [2 + 2] Cycloaddition Relay Enabled C-C Triple Bond Cleavage of Yne-Allenones

An unusual catalytic double [2 + 2] cycloaddition relay reaction of yne-allenones with unactivated alkenes and alkynes has been achieved, which enabled C-C triple-bond cleavage to access more than 60 examples of functionalized phenanthren-9-ols with generally good yields. This reaction provides a regioselective and practical method for the construction of carbocyclic ring systems with a high degree of functional group compatibility. Aside from surveying the scope of this transformation, mechanistic details of this process are provided by conducting systematic theoretical calculations.

Donor- and acceptor-enynals/enynones

Three kinds of transformations based on benzo-fused donor- and acceptor-enynals/enynones, including reactions with alkenes, alkynes, and H₂O, were discussed.

Selectivity-switchable construction of benzo-fused polycyclic compounds through a gold-catalyzed reaction of enyne-lactone

A gold-catalyzed selectivity-switchable reaction of enyne-lactone is reported. The choice of the gold complex is the key for the chemoselectivity.

Lewis Acid-Catalyzed Selective [2 + 2]-Cycloaddition and Dearomatizing Cascade Reaction of Aryl Alkynes with Acrylates

Combined Lewis acid, consisting of two or more Lewis acids, sometimes shows unique catalytic ability, and it may promote reactions which could not be catalyzed by any of the Lewis acids solely. On the other hand, the development of efficient methods for the facile synthesis of cyclobutenes and densely functionalized decalins is an attractive target for synthetic chemists due to their versatile synthetic utilities and widespread occurrence in natural products. Herein, we wish to report an efficient method for the assembly of cyclobutenes and densely functionalized decalin skeletons through In(tfacac)₃-TMSBr catalyzed selective [2 + 2]-cycloaddition and dearomatizing cascade reaction of aryl alkynes with acrylates with high chemo- and stereoselectivity. The obtained cyclobutene could be easily converted into cyclobutane as well as synthetically useful 1,4- and 1,5-diketones with high chemo- and stereoselectivity. On the basis of mechanistic studies, plausible reaction mechanisms were proposed for both the [2 + 2]-cycloaddition and the dearomatizing cascade reaction. Finally, the computational studies of reaction mechanisms were conducted, and the results suggest that the combined Lewis acid could efficiently promote both reactions.

An efficient approach to generate aryl carbenes: gold-catalyzed sequential activation of 1,6-diynes

An efficient approach to generate aryl gold carbenes has been developed.

Gold-catalyzed ring-expansion through acyl migration to afford furan-fused polycyclic compounds

A gold-catalyzed ring-expansion reaction of alkynones to access furan-fused polycyclic compounds is reported.

Silver-Catalyzed Domino Reaction of ortho-Carbonylated Alkynyl-Substituted Arylaldehydes with Conjugated Dienes: Stereoselective Access to Indanone-Fused Cyclohexenes

A silver-catalyzed domino reaction of ortho-carbonylated alkynyl-substituted arylaldehydes with conjugated dienes is described here. Through this reaction, the synthesis of a variety of indanone-fused cyclohexene derivatives can be achieved efficiently. The formation of these tricyclic products could involve a key Diels-Alder reaction of in situ generated indanenone dienophiles with conjugated dienes. Particularly, the products can be accomplished in a high endo/exo selective way.

Selectivity-switchable oxidation of tetraarylethylenes to fused polycyclic compounds

Selectivity-switchable oxidation of furan-containing tetraarylethylenes is reported.