Cellulose-SO3H: an efficient and biodegradable solid acid for the synthesis of quinazolin-4(1H)-ones

The condensation of 2-aminobenzamide with aldehydes or ketones has been achieved using cellulosesulfonic acid under mild reaction conditions to furnish 2,3-dihydroquinazolin-4(1H)-ones in good yields with a high selectivity. The use of biodegradable solid acid catalyst, cellulosesulfonic acid makes this method quite simple, more convenient, and practical. This catalyst was also found to be very active for the synthesis of hydroxyalkylquinazolin-4-ones from cyclic enol ethers.     

Highly stereocontrolled synthesis of fluorinated 2,6-trans dihydropyrans via Prins cyclization

A highly efficient method for the synthesis of fluorinated 2,6-trans dihydropyrans via BF₃·Et₂O-promoted Prins cyclization of allenic alcohols and aldehydes is developed. Various 2,6-trans fluorodihydropyrans are obtained in moderate to good yields with excellent diastereoselectivities.     

HBF4·OEt2 as a versatile reagent for the Hosomi-Sakurai allylation and Prins cyclization: one-pot synthesis of symmetrical 4-fluorotetrahydropyrans

The synthesis of symmetrical 2,6-disubstituted 4-fluorotetrahydropyran derivatives has been achieved using HBF₄·OEt₂ via a tandem allylation and Prins cyclization. This is a highly efficient and diastereoselective approach for the preparation of 4-fluorotetrahydropyrans in a single step. The use of readily available and easy to handle reagent HBF₄·OEt₂ makes this method simple, convenient and practical.     

A concise stereoselective formal total synthesis of the cytotoxic macrolide (+)-Neopeltolide via Prins cyclization

A convergent and highly stereoselective formal total synthesis of the naturally occurring, cytotoxic 14-membered macrolide neopeltolide has been achieved via two Prins cyclizations.     

BF3-Et2O mediated biogenetic type synthesis of chromanochalcones from prenylated chalcones via a regioselective cyclization reaction

In continuation of our program on synthetic chalcones, we have developed a simple and convenient method for the synthesis of chromanochalcones from prenylated chalcones in high yields by regioselective cyclization using BF₃-Et₂O.     

Stereoselective syntheses of (−)-tetrahydrolipstatin via Prins cyclisations

Stereoselective syntheses of (−)-tetrahydrolipstatin have been achieved via two divergent approaches through Prins cyclisations as the key steps. PCC mediated oxidative cleavage, Frater alkylation, Keck allylation, Sharpless asymmetric epoxidation and allylic cleavage were the other key steps employed.     

Total synthesis of cryptophycin-24 (arenastatin A) via Prins cyclization

A stereoselective synthesis of fragment A of cryptophycin is achieved utilizing the versatile Prins cyclization. Subsequently, the total synthesis of cryptophycin-24 (arenastatin A) has been accomplished by coupling it with the depsipeptide subunit.     

Lewis acid-catalyzed one-pot crossed Prins cyclizations using allylchlorosilane as allylating agent

A one-pot multi-component Lewis acid-catalyzed Prins cyclization was developed with high yield and selectivity. The crossed 2,4,6-trisubstituted tetrahydropyran products were formed with high stereoselectivity. This catalytic method could also be used with α,β-unsaturated aldehydes affording moderate yields of products.     

An efficient approach to the synthesis of 3-vinylidene tetrahydropyrans via Prins-type cyclization

Lewis acid-catalyzed intramolecular reactions of oxocarbenium ions with propargylsilanes are described. The results obtained indicate that trimethylsilyl trifluoromethanesulfonate (TMSOTf) efficiently catalyses cyclization leading to the corresponding 3-vinylidene tetrahydropyrans in high yield as single isomers.     

Stereochemical Prins cyclization: electronic versus steric effects on the synthesis of 2,4,6-trisubstituted tetrahydropyran rings

A convenient approach towards the synthesis of both syn- and anti-2,4,6-chlorotetrahydropyrans has been developed. The electronic and steric influences on the stereochemistry of the Prins cyclized products were investigated based on the substituents of the homoallylic alcohol.     

Efficient Prins cyclization in environmentally benign method using ion exchange resin catalyst

Abstract

Amberlyst-15^® (H⁺) resin catalyzes efficient one-pot solvent free Prins cyclization of an aldehyde and a homoallylic alcohol to yield dihydropyrans and 4-hydroxytetrahydropyrans. The products, which display interesting olfactory property, are obtained under mild condition and by simple work up. The recovered resin can be used repeatedly .     

A convergent route to β-hydroxy δ-lactones through Prins cyclisation as the key step: synthesis of (+)-prelactones B, C and V

Reactions of homoallylic alcohols with aldehydes in the presence of acid catalysts gave multisubstituted tetrahydropyrans with the creation of one to three new stereogenic centres in a single-pot process. The utility of this approach is extended to the enantioselective syntheses of (+)-prelactones B, C and V.     

Application of Prins cyclization to the total synthesis of (+)-decytospolides A and B

(+)-Decytospolides A and B, natural products containing the tetrahydropyran skeleton, were synthesized via Prins cyclization as the key step.     

Convenient synthesis of highly optically active 2,3,4,6-tetrasubstituted tetrahydropyrans via Prins cyclization reaction (PCR) of optically active homoallylic alcohols with aldehydes

Prins cyclization reaction (PCR) of optically active homoallylic alcohols, R^aC^*H(OH)CH₂CHCHCH₃ (1-substituted but-2-en-1-ol), with aldehydes (R^bCHO) in the presence of an acid-catalyst (HX) affords (2-R^b,3-CH₃,4-X,6-R^a)-tetrasubstituted tetrahydropyrans highly stereoselectively in good yields.     

Total synthesis of (+/−)-diospongin A via Prins reaction

A straightforward synthesis of (+/−)-diospongin A starting from benzaldehyde is described. A Prins cyclization reaction to control the relative configuration of the three stereogenic centers and a Mitsunobu inversion represent the key steps of the approach.     

Synthesis of 3,4-dihydropyridin-2-one derivatives in convergent mode applying bio catalyst vitamin B1 and polymer supported catalyst PEG-SO3H from two different sets of building blocks

Two highly efficient, green protocols have been developed for the synthesis of 3,4-dihydropyridin-2-one derivatives from different starting materials exploring two reaction specific catalysts, vitamin B₁ (VB₁), and PEG-SO₃H. VB₁ catalyzed simple and convenient protocol has been developed for the synthesis of 3,4-dihydropyridin-2-one derivatives by the installation of aldehyde, cyanoacetamide, and 1,3-dicarbonyl compounds. In addition, 3,4-dihydropyridin-2-one derivatives have also been synthesized by simply combining aldehyde, malononitrile, and 1,3-dicarbonyl compounds via the formation of 4H-pyran nucleus and PEG-SO₃H catalyzed one-pot rearrangement.     

FeCl3-SiO2 as a reusable heterogeneous catalyst for the synthesis of 5-substituted 1H-tetrazoles via [2+3] cycloaddition of nitriles and sodium azide

An efficient method for the preparation of 5-substituted 1H-tetrazole derivatives is reported using FeCl₃-SiO₂ as an effective heterogeneous catalyst. This method has the advantages of high yields, simple methodology, and easy work-up. The catalyst can be recovered by simple filtration and reused delivering good yields.     

Polymeric ionic liquid as novel catalyst for the Prins reaction

A series of micro-mesoporous polymeric ionic liquids (PILs) have been successfully synthesized by the method of anion and cation copolymerization. Then use FT-IR, N₂ adsorption–desorption isotherms, SEM, and TG to characterize them. Furthermore, the catalytic performance of the synthesized PILs was investigated for the Prins reaction of propylene with 1, 3, 5-trioxane. Among the four PILs synthesized, VIMBs-DVB-SSA has better catalytic activities for the Prins reaction. Under the optimal conditions, 100 °C, 8 wt%, 4 h and n (propylene)/n (1, 3, 5-trioxane) = 4:1, the conversion of formaldehyde (99.8%) and selectivity (81.7%) for 4-methyl-1, 3-dioxane. In addition, the effects of reaction time, catalyst dosage, and reaction temperature and mole ratio of reaction substrates on the reaction were also investigated. The prepared catalyst had good thermal stability and can be reused easily.     

Stereoselective synthesis of anti-2-oxazolidinones by Ph3P-CCl4-Et3N mediated SN2 cyclization of N-Boc-β-amino alcohols

Ethyl anti-4-substituted phenyl-2-oxo-1,3-oxazolidine-5-carboxylates were synthesized stereoselectively in excellent yields using the Ph₃P-CCl₄-Et₃N system by S_N2 cyclization of N-Boc-β-amino alcohols. syn to anti conversion of ethyl 4-substituted phenyl-2-oxo-1,3-oxazolidine-5-carboxylates using DBU as base is also described.     

An efficient and convenient protocol for the synthesis of quinoxalines and dihydropyrazines via cyclization-oxidation processes using HClO4·SiO2 as a heterogeneous recyclable catalyst

A convenient and straightforward method has been developed for the synthesis of quinoxalines and dihydropyrazines (DHPs) using α-bromo ketones and 1,2-diamines in the presence of silica supported perchloric acid (HClO₄·SiO₂) at room temperature. The quinoxalines and DHPs were presumably formed via cyclization-oxidation. The catalyst works under heterogeneous conditions and can be recycled.