Evidence for pi-stacking as a source of stereocontrol in the synthesis of the core pyranochromene ring system common to calyxin I, calyxin J, and epicalyxin J

Intramolecular/Intermolecular Sequential Cyclization Accompanied by Double C-F Bond Cleavage: Access to Tricyclic Fluorine-Containing Pyrano[3,2-c]chromenes

Defluorinative cyclization of CF3-alkenes has emerged as a reliable strategy for crafting intricate polycyclic frameworks. In this study, a facile defluorinative bicyclization approach was developed for the construction of 4H,5H-pyrano[3,2-c]chromenes under mild conditions involving a sequence of intramolecular cyclization and intermolecular defluoroheterocyclization. A variety of polysubstituted 4H,5H-pyrano[3,2-c]chromenes featuring C2-fluorine could be synthesized in good yields with excellent tolerance toward various functional groups. Moreover, the introduction of a C-F bond provides additional possibilities for further modification of this skeleton. The product features aggregation-induced emission (AIE) characteristics after simple modification, which is promising for chemical and biomedical imaging.

A nickel(ii)-catalyzed asymmetric intramolecular Alder-ene reaction of 1,7-dienes

A highly diastereo- and enantioselective intramolecular Alder-ene reaction with an alkene as the enophile has been developed by using a chiral N,N'-dioxide/nickel(ii) complex as the catalyst. This protocol provides a facile route towards the synthesis of diverse 3,4-disubstituted chroman, tetrahydroquinoline, piperidine and thiochroman derivatives in high yields with good to excellent diastereo- and enantioselectivities.

A Base-Catalyzed, Domino Aldol/hetero-Diels-Alder Synthesis of Tricyclic Pyrano[3,4-c]chromenes in Glycerol

The domino aldol/hetero-Diels-Alder synthesis of some new tricyclic pyrano[3,4-c]chromene derivatives has been achieved successfully after assembling a variety of acyclic or cyclic monoketones with prenyl ether-tethered aldehydes in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene in glycerol at 120 °C. The hitherto unreported stereochemical outcome of this synthetic sequence was studied and established on the basis of single-crystal X-ray diffraction data and 2D NMR NOESY spectroscopy along with the isolation and characterization of the intermediate Aldol condensation product.

Stereoselective construction of functionalized tetracyclic and pentacyclic coumarinopyranpyrazole/pyrimidinedione/coumarin scaffolds using a solid-state melt reaction

An assembly of tetra / pentacyclic hybrid scaffolds have been synthesized for the first time using a solid-state melt reaction in a stereoselective fashion with excellent yields.

Titanocene-catalyzed multicomponent coupling approach to diarylethynyl methanes

A titanocene-catalyzed multicomponent coupling to provide diarylethynyl methanes is described. By combining the multifunctionality of Cp(2)TiCl(2) with the traceless dielectrophilicity of aryl aldehydes, all-carbon tertiary centers are obtained in 55-99% yield.

Superelectrophiles and the effects of trifluoromethyl substituents

Trifluoromethyl-substituted superelectrophiles were generated in superacid (CF(3)SO(3)H), and their chemistry was examined. The strong electron-withdrawing properties of the trifluoromethyl group are found to enhance the electrophilic character at cationic sites in superelectrophiles. This leads to greater positive-charge delocalization in the superelectrophiles. These effects are manifested by the unusual chemo-, regio-, and stereoselectivities shown by the superelectrophiles in chemical reactions.