Synthesis of Tetrahydrofuran and Tetrahydropyran Derivatives Catalyzed by Tungstophosphoric Acid in Ionic Liquid

Synthesis of tetrahydrofuran and tetrahydropyran derivatives catalyzed by tungstophosphoric acid （H3PW12040） were conveniently performed with high yield from the corresponding unsaturated alcohols in ionic liquid. Sufuric acid （H2SO4）, trifluoromathanesulfonic acid （TfOH） and p-toluenesulfonic acid （TsOH） were also explored for preparing these products in ionic liquid. The catalysts and ionic liquid can be easily recovered and reused.

Prins cyclisation of (-)-isopulegol with benzaldehyde over ZSM-5 based micro-mesoporous catalysts for production of pharmaceuticals

Several ZSM-5 derived micro-mesoporous catalysts were investigated in Prins cyclisation of (-)-isopulegol with benzaldehyde acting as a reactant and a solvent for production of heterocyclic oxygen containing 2H-chromene derivatives including the tetrahydropyran structure and exhibiting biological activity. The investigated catalysts were characterized by nitrogen adsorption, ammonia temperature programmed desorption, adsorption-desorption of pyridine and 2,6-di-tert- butylpyridine with Fourier transform infrared spectroscopic control. For the Prins reaction performed at 70℃, the highest yield of the desired product, equal to 67% at complete conversion of (-)-isopulegol, was obtained over a micro-mesoporous catalyst containing an optimum amount of strong acid sites and mesopores, being 12 fold larger than the size of the desired product.

A Novel Method for Synthesis of Tetrahydropyrane and Piperidine Derivatives

Piperidine-4-ones and tetrahydropyrane-4-ones are important precursors for the synthesis of functionally substituted piperidines and tetrahydropyranes. In this study, the condensation of hexa-2, 4-diene and 2-methyl-penta-2, 4-diene with formaldehyde （reaction of oxymethylation） was investigated. The functionally substituted derivatives of piperidine and tetrahydropyrane were synthesized. The comparison of oxymethylation of dienes and 1-alkenes was showed, which indicates that the highest yield of tetrahydropyrane derivatives was achieved with 1-alkenes. This study provided theoretical basis for the synthesis of piperidine and tetrahydropyrane derivatives.

Two types of coumarins-specific enzymes complete the last missing steps in pyran- and furanocoumarins biosynthesis

Pyran-and furanocoumarins are key representatives of tetrahydropyrans and tetrahydrofurans,respectively,exhibiting diverse physiological and medical bioactivities.However,the biosynthetic mechanisms for their core structures remain poorly understood.Here we combined multiomics analyses of biosynthetic enzymes in Peucedanum praeruptorum and in vitro functional verification and identified two types of key enzymes critical for pyran and furan ring biosynthesis in plants.These included three distinct P.praeruptorum prenyltransferases(PpPT1e3)responsible for the prenylation of the simple coumarin skeleton 7 into linear or angular precursors,and two novel CYP450 cyclases(PpDC and PpOC)crucial for the cyclization of the linear/angular precursors into either tetrahydropyran or tetrahydrofuran scaffolds.Biochemical analyses of cyclases indicated that acid/base-assisted epoxide ring opening contributed to the enzyme-catalyzed tetrahydropyran and tetrahydrofuran ring refactoring.The possible acid/base-assisted catalytic mechanisms of the identified cyclases were theoretically investigated and assessed using site-specific mutagenesis.We identified two possible acidic amino acids Glu303 in PpDC and Asp301 in PpOC as vital in the catalytic process.This study provides new enzymatic tools in the epoxide formation/epoxide-opening mediated cascade reaction and exemplifies how plants become chemically diverse in terms of enzyme function and catalytic process.

GaI_3 Catalyzed Tetrahydropyranylation of Alcohols and Phenols

In dichloromethane, the nucleophilic addition of alcohols or phenols to 3,4-dihydro-2H-pyran (DHP) was cata-lyzed effectively by gallium triiodide which was generated in situ by the reaction of gallium metal and iodine to give the corresponding tetrahydropyranyl acetals in good to excellent yields.

One-pot tandem Barbier-Prins synthesis of tetrahydropyrans in aqueous media

By investigating the effect of the amount of water, the ratio of aldehyde and allyl- bromide, and the reaction temperature on the transformation, 2,4,6-trisubstituted tetrahydro- pyrans are synthesized by a novel tandem Barbier-Prins-cyclization reaction in the presence of micro-amount of water under mild conditions. The experiment is easy to perform without the need to exclude moisture or air. The reaction is atomic economical and environmentally benign.

An Efficient Prins Cyclization for Stereoselective Synthesis of Tetrahydropyran from Imines and Homoallyl Alcohols

An unprecedented protocol has been developed for the efficient synthesis of substituted tetrahydropyrans via a bismuth-promoted Prins cyclization of imines with homoallyl alcohols.In the presence of 40 mol%BiCl_(3),a wide variety of imines react smoothly with homoallyl alcohols at room temperature to give the corresponding 4-chlorotetrahydropyran derivatives in good to excellent yields.

Asymmetric synthesis of tetrahydropyran[3,2-c]quinolinones via an organocatalyzed formal[3+3]annulation of quinolinones and MBH 2-naphthoates of nitroolefin

An efficient asymmetric and enantio-swithchable organocatalytic[3+3]annulation reaction using MBH-2-naphthoates of nitroalkenes and 4-hydroxyquinolin-2(1H)-ones has been developed.Densely substituted tetrahydropyrano[3,2-c]qui noli nones scaffolds with two adjacent stereogenic centers are obtained with high yield(up to 95%yield)and good stereoselectivities(up to>20:1 dr and 96%ee)in an enantio-switchable manner.Furthermore,gram scale synthesis was achieved and the nitro group could easily transform into an amino group without any appreciable loss in the diastereo-and enantioselectivity.

TBAF-catalyzed cyclization of 6-hydroxyhex-2-ynoates and 7-hydroxyhept-2-ynoates

Tetrabutyl ammonium fluoride（TBAF） was found to be capable of catalyzing the intramolecular hydroalkoxylation of 6- hydroxyhex-2-ynoates and 7-hydroxyhept-2-ynoates.The reaction could be used to prepare 2,5-substituted THF rings and 2,6- substituted THP rings.