Synthesis of polycyclic indoles via organocatalytic bicyclization of α-alkynylnaphthalen-2-ols with nitrones

Cinchonidine-Catalyzed Synthesis of Oxazabicyclo[4.2.1]nonanones from N-Aryl-α,β-unsaturated Nitrones and 1-Ethynylnaphthalen-2-ols

A variety of oxazabicyclo[4.2.1]nonanone derivatives were prepared in good yields through a cinchonidine-catalyzed cascade reaction of N-aryl-α,β-unsaturated nitrones and 1-ethynylnaphthalen-2-ols. Mechanistic studies show that the reaction undergoes a [4 + 3] cycloaddition of nitrones to vinylidene o-quinone methide generated in situ from 1-ethynylnaphthalen-2-ols in the presence of cinchonidine, 1,3-rearrangement of N-O vinyl moieties, ring-opening, and finally double intramolecular cyclizations to afford oxazabicyclo[4.2.1]nonanones over five steps in a one-pot reaction.

Synthesis of aryl-fused 1,4-oxathiepines from pyridinium 1,4-zwitterionic thiolates and vinylidene ortho-quinone methides

Synthesis of aryl-fused 1,4-oxathiepines from pyridinium 1,4-zwitterionic thiolates with vinylidene ortho-quinone methides generated in situ via a formal (3 + 4) pathway.

2-Indolymethanols as 4-atom-synthons in oxa-Michael reaction cascade: access to tetracyclic indoles

The first Brønsted acid-catalyzed oxa-Michael reaction cascade of 2-indolylmethanols with trione alkenes was accomplished. By using this practical approach, a variety of tetracyclic indoles were readily created in an ordered sequence with excellent regio- and diastereoselectivity. 2-Indolylmethanols commendably served as four-atom synthons, as opposed to the common three-atom synthons in the previous literature reports. The regioselectivity issue was well handled by the employment of a strong Brønsted acid catalyst. In addition, its dual role in activation of substrates via hydrogen-bonding interaction and acceleration of subsequent intramolecular cyclization and dehydration was proposed to account for the high reaction efficiency.

Gold-Catalyzed Tandem Annulations of Pyridylhomopropargylic Alcohols with Propargyl Alcohols

A gold-catalyzed tandem annulation of propargylic alcohols and pyridylhomopropargylic alcohols is achieved, providing an atom-economical approach to a diverse set of polycyclic dihydrobenzofurans in good yields. The reaction proceeds via the 5-endo-dig cyclization/Meyer-Schuster rearrangement/Friedel-Crafts-type pathway. In this way, three C-C bonds and one C-O bond form to give a polycyclic skeleton in a one-pot process. Moreover, the products exhibit unique optical properties, which reveal their potential application value.

Sc(OTf)3-catalyzed [3 + 2]-cycloaddition of nitrones with ynones

An efficient approach to access functionalized (2,3-dihydroisoxazol-4-yl) ketones has been developed by reacting nitrones 4 with ynones 7 or terminal ynones 10 in a one-pot fashion. The reaction went through a formal Sc(OTf)3-catalyzed [3 + 2]-cycloaddition process to generate a number of functionalized (2,3-dihydroisoxazol-4-yl) ketones 11aa-11aw, 11ba-11la and 12aa-12ae in moderate to good yields.

Synthesis of C3-alkylated benzofurans via palladium-catalyzed regiocontrolled hydro-furanization of unactivated alkenes

A new chelation-controlled hydrofuranization of unactivated olefins with α-alkynyl arylols is reported for the first time, and used to produce a wide range of C₃-alkylated benzofurans with generally good yields under mild conditions.