On the basis of the Lewis acid-catalyzed Friedel–Crafts alkylation between 1-acyl-2-arylcyclopropanecarboxylate esters and electron-rich phenols, a Sc(OTf)3 catalyzed cascade [4 + 2]-annulation reaction was developed for the direct synthesis of polysubstituted dihydronaphthols from phenols. In this reaction, the structure of products is dominated by the directing effect of the substituent groups on phenols. Meanwhile, a one-pot Friedel–Crafts alkylation/oxidative cyclization reaction was also developed for the synthesis of spiro-fused 2,5-cyclohexadienones.

A novel strategy was developed for the application of Rh carbenes generated from readily accessible N-sulfonyl 1,2,3,-triazoles or diazocompouds in the high order cycloadditions, which offered an efficient route to a variety of N-containing medium-sized rings. The process provided a wide range of cyclohepta[b]pyrazine and cyclohepta[b]pyrrolone derivatives with high yields.

A Lewis acid catalyzed [3+4]-annulation reaction between cyclopropane 1,1-diesters and anthranils has been developed. This annulation consists of a reaction sequence involving ring-opening/aromatization/nucleophilic addition. Thereinto, aromatization is the driving force for this annulation. Using this reaction, a series of 8-oxa-1-azabicyclo[3.2.1]octanes can be prepared conveniently with excellent diastereoselectivity.

•Synthesized graphene oxide improves the flotation recovery of pentlandite in pentlandite/serpentine flotation system.•Graphene oxide acts as both a dispersant and a flocculant for serpentine in the flotation separation.•Graphene oxide might be a potential depressant in froth flotation of sulfides.This paper studied the effects of graphene oxide (GO) on the slime coatings of serpentine in the flotation of pentlandite. The flotation results showed that the flotation recovery of pentlandite was improved with the addition of GO, compared with carboxymethyl cellulose (CMC). The possible mechanisms of the improved flotation recovery were investigated by electrokinetic study, FTIR study, sedimentation tests and scanning electronic microscopy (SEM) analysis. The experimental results demonstrated that both of the two depressants dispersed the hydrophilic serpentine particles from the pentlandite surface. For GO, however, the flocculation of serpentine was a further reason responsible for the enhanced recovery of pentlandite.Proposed model for the changes of pentlandite/serpentine system in deionized water (A) and in GO solution (B).Download high-res image (177KB)Download full-size image

A catalytic [3 + 1]-annulation reaction between cyclopropane 1,1-diester and aromatic amine is developed based on the relay catalysis strategy. Lewis acid-catalyzed nucleophilic ring opening of cyclopropane 1,1-diester with aromatic amine and (hypo)iodite-catalyzed C–N bond formation are combined successfully in one reaction. Using this reaction, biologically important azetidines and tetrahydroquinolines can be prepared directly.

A TiCl4 promoted formal [3 + 3] cycloaddition of cyclopropane 1,1-diesters with azides has been developed for the synthesis of highly functionalized triazinines. Both stoichiometric and substoichiometric versions of this reaction were accomplished dependent on the choice of solvent. It is noteworthy that the corresponding products could be easily converted to biologically important azetidines by simple thermolysis.

An enantioselective cascade Michael–Michael reaction between chalcones enolates and nitromethane catalyzed by a bifunctional thiourea is developed. This reaction provides a mild but efficient approach to chiral benzopyrans bearing three consecutive stereocenters in high yields with excellent stereoselectivities, and the benzopyrans can be easily transformed to the corresponding tricyclic product.

A Lewis acid catalyzed [3+4]-annulation reaction between cyclopropane 1,1-diesters and anthranils has been developed. This annulation consists of a reaction sequence involving ring-opening/aromatization/nucleophilic addition. Thereinto, aromatization is the driving force for this annulation. Using this reaction, a series of 8-oxa-1-azabicyclo[3.2.1]octanes can be prepared conveniently with excellent diastereoselectivity.