[4 + 2]-Cycloaddition and 1,4-Addition of ortho-Quinone Methides by a Chiral Crotyl Silane

Rh(III)-catalyzed (5 + 2)-cycloaddition reactions of ortho-hydroxyethyl phenols with internal alkynes: efficient synthesis of benzoxepines

An unprecedented (5 + 2)-cycloaddition reaction of ortho-hydroxyethyl phenol and internal alkyne was developed. This Rh(III)-catalyzed reaction provided benzoxepine derivatives which have very high biological significance. A wide range of ortho-hydroxyethyl phenols and internal alkynes were studied to provide the benzoxepines in high yields.

Asymmetric Synthesis of Chromans Through Bifunctional Enamine-Metal Lewis Acid Catalysis

Cooperative enamine-metal Lewis acid catalysis has emerged as a powerful tool to construct carbon-carbon and carbon-heteroatom bond forming reactions. A concise synthetic method for asymmetric synthesis of chromans from cyclohexanones and salicylaldehydes has been developed to afford tricyclic chromans containing three consecutive stereogenic centers in good yields (up to 87 %) and stereoselectivity (up to 99 % ee and 11 : 1 : 1 dr). This difficult organic transformation was achieved through bifunctional enamine-metal Lewis acid catalysis. It is believed that the strong activation of the salicylaldehydes through chelating to the metal Lewis acid and the bifunctional nature of the catalyst accounts for the high yields and enantioselectivity of the reaction. The absolute configurations of the chroman products were established through X-ray crystallography. DFT calculations were conducted to understand the mechanism and stereoselectivity of this reaction.

Redox-triggered dearomative [5 + 1] annulation of indoles with O-alkyl ortho-oxybenzaldehydes for the synthesis of spirochromanes

The dearomative [5 + 1] annulation of 2-methylindoles with new five-membered synthon was developed through cascade [1,5]-hydride transfer/dearomative cyclization in HFIP for the synthesis of spirochromanes bearing the 2-methylindolenine skeleton.

Catalytic Asymmetric [4 + 2] Cycloaddition of ortho-Alkenyl Naphthols/Phenols with ortho-Quinone Methides: Highly Stereoselective Synthesis of Chiral 2,3,4-Trisubstituted Chromans

Chiral phosphoric acid-catalyzed biomimetic asymmetric [4 + 2] cycloaddition of ortho-alkenyl naphthols/phenols and ortho-quinone methides (o-QMs) has been demonstrated to afford various important 2,3,4-trisubstituted chromans in high yields with excellent enantio- and diastereoselectivities (up to 99% yield, 99% ee, >20:1 dr). Notably, this methodology not only enabled access to the trans-cis chiral trisubstituted chromans from 1-alkenyl 2-naphthols but also is compatible with 2-alkenyl 1-naphthols and phenols to deliver trans-trans chiral trisubstituted chromans.

Cu(ii)-Catalyzed formal [4 + 2] cycloaddition between quinone methides (QMs) and electron-poor 3-vinylindoles

A new Cu(ii)-catalyzed formal [4 + 2] cycloaddition between quinone methides (QMs) including para-quinone methides (p-QMs) and ortho-quinone methides (o-QMs) and electron-poor 3-vinylindoles was established.

Lewis Acid Catalyzed [4 + 2] Cycloaddition of N-Tosylhydrazones with ortho-Quinone Methides

A formal [4 + 2] cycloaddition of N-tosylhydrazones with ortho-quinone methides was developed, affording the facile synthesis of diverse 1,3-oxazine derivatives under mild conditions. In this transformation, N-tosylhydrazones are used as a 1,2-dipole synthon under base-free conditions. Moreover, the substrate scope is broad, and the products are formed with high diastereoselectivities in most of the cases.