Selectivity enhancement of silica-supported sulfonic acid catalysts in water by coating of ionic liquid

Coating of silica-supported sulfonic acid catalysts with hydrophobic ionic liquid leads to a significant improvement of catalyst selectivity. Many organic reactions, including Prins cyclization, cycloaddition of epoxide to aldehyde, and dehydrative etherification of secondary benzyl alcohols, proceed well in formalin or pure water. In particular, tandem dehydration/Prins cyclization reactions of tertiary and secondary alcohols with formaldehyde were developed for the first time.     

o-Benzenedisulfonimide as a Recyclable Homogeneous Organocatalyst for an Efficient and Facile Synthesis of 4-Amidotetrahydropyran Derivatives Through Prins–Ritter Reaction

A highly diastereoselective synthesis of 4-amidotetrahydropyran derivatives has been achieved using a catalytic amount of o-benzenedisulfonimide under mild conditions involving sequential allylation and Prins–Ritter amidation. The oxo-carbenium ion formed in Prins cyclization could be successfully trapped with nitriles through Ritter amidation. The catalyst is highly efficient in promoting both allylation and Prins cyclization with a net addition of nitrile. The catalyst can be easily recovered and reused in subsequent reactions.     

Prins cyclization for the preparation of 2-isobutyl-4-methyl-tetrahydro-<Emphasis Type="Italic">2H</Emphasis>-pyran-4-ol using supported heteropoly acids

The selective preparation of 2-isobutyl-4-methyl-tetrahydro-2H-pyran-4-ol (also called Florosa or Florol) was performed. Prins cyclization of isoprenol and isovaleraldehyde was used for the preparation of this important fragrant compound. Heteropoly acids (phosphotungstic and phosphomolybdic) were used as a catalyst in homogeneous and also in heterogeneous arrangements (after their immobilization). The only solvent necessary for the reaction was water that enables the increase of the selectivity to the desired product by hydrolysis of catalyst-carbocation intermediates. In a flow, both heteropoly acids were successfully anchored on siliceous MCM-41 and resultant materials were characterized by XRF, XRD, SEM, FTIR, UV–Vis, and nitrogen adsorption. Heterogenization was performed in water as a solvent. Anchored heteropoly acids were used in Prins cyclization under the same conditions (addition of water), and the selectivity was even higher (96 %), comparing the homogeneous arrangement. No leaching of catalyst from solid was observed. Moreover, the catalyst may be reused without loss of activity and selectivity at least four times.     

Synthesis of (-)-centrolobine by Prins cyclizations that avoid racemization

[formula: see text] The segment-coupling Prins cyclization avoids two of the problems common to other Prins cyclization protocols: side-chain exchange and partial racemization by reversible 2-oxonia Cope rearrangement. Model studies demonstrate the stereochemical fidelity of Prins cyclizations using alpha-acetoxy ethers compared with direct aldehyde-alcohol Prins reactions. Furthermore, we propose a mechanism for the racemization observed in some intermolecular Prins cyclizations. Two straightforward syntheses of optically pure (-)-centrolobine highlight the utility of Prins cyclizations.     

Cellulose-SO3H as a recyclable catalyst for the synthesis of tetrahydropyranols via Prins cyclization

Tetrahydropyranols are prepared in good yields and with high cis-selectivity by means of the Prins cyclization using cellulose-sulfonic acid under mild reaction conditions. This is the first report on the preparation of tetrahydropyranols using epoxides and homoallylic alcohols via Prins cyclization.     

BiX3 and FeX3‐Promoted Prins Cyclization of Enol Ethers in CH2Cl2

The Prins cyclization of enol ethers has been realized by employing BiX₃ (or FeX₃) as catalyst and TMSX (X=Br, Cl) as the halogen source. The presence of a tiny amount of water in the solvent dichloromethane played a key role for the reaction to proceed. The reaction is believed to be catalyzed by Lewis acid‐assisted Brønsted acids, which were generated in situ from MX₃ and water in the solvent.     

The Organocatalytic Asymmetric Prins Cyclization

We describe here the design and development of an organocatalytic Prins cyclization. In the presence of a confined chiral imidodiphosphoric acid catalyst, salicylaldehydes react with 3‐methyl‐3‐buten‐1‐ol to afford highly functionalized 4‐methylenetetrahydropyrans in excellent regio‐ and enantioselectivity. The extreme steric demand of the acid catalyst is key for the success of this transformation.     

Brønsted acid-promoted domino reactions: a novel one-pot three-component synthesis of 3,4,5-trisubstituted-3,6-dihydro-2H-1,3-oxazines

An efficient and novel one-pot synthesis of 3,4,5-trisubstituted-3,6-dihydro-2H-1,3-oxazine from alkynoates, anilines, and formaldehyde is described. The six-membered N,O-heterocyclic skeleton was constructed via Brønsted acid-promoted domino hydroamination/Prins reaction/cyclization/dehydration reactions.     

The silylalkyne-Prins cyclization: stereoselective synthesis of tetra- and pentasubstituted halodihydropyrans

[reaction: see text] A new type of Prins cyclization using silylated secondary homopropargylic alcohols and aldehydes yielding tetra- and pentasubstituted dihydropyrans is described. The presence of the trimethylsilyl group in the triple bond favors the Prins cyclization and minimizes the 2-oxonia-[3,3]-sigmatropic rearrangement as a competitive alternative pathway. Ab initio theoretical calculations of the species involved in the rearrangements support the proposed mechanism. The process is highly stereoselective, affording cis-dihydropyran as the only isomer.     

Prins cyclizations in silyl additives with suppression of epimerization: versatile tool in the synthesis of the tetrahydropyran backbone of natural products

[reactions: see text] A catalytic Prins cyclization reaction has been developed. The involvement of trimethylsilyl halides offers a versatile route to the formation of cis-4-halo-2,6-disubstituted tetrahydropyran rings. The problem of epimerization in Prins cyclization has also been addressed in the total synthesis of (-)-centrolobine using this methodology.     

功能化酸性离子液体催化甲醛与烯烃的Prins缩合反应

研究了以功能化酸性离子液体为催化剂,甲醛与烯烃Prins缩合反应生成1,3-二噁烷及其衍生物,水解得到1,3-二元醇.对不同结构的离子液体、催化剂用量和反应条件进行了考察.结果表明,该体系具有良好的催化性能,反应可在较温和的条件下进行,实现了高活性和高选择性的目标.产物易分离,催化剂重复使用6次,其催化活性基本不变.     

Total synthesis of 7-desmethoxyfusarentin and its methyl ether

A concise total synthesis of 7-desmethoxyfusarentin and its methyl ether has been accomplished involving a sequence of reactions such as Prins cyclization, ring opening of tetrahydropyran ring and Alder-Rickerts reaction as key steps. This is the first report on the construction of anti-1,3-diol unit of 7-desmethoxyfusarentin by means of Prins cyclization.     

Unprecedented synergistic effects between weak Lewis and Brønsted acids in Prins cyclization

Novel synergistic effects between Lewis and Br?nsted acids in Prins cyclization are reported. Non-reactive Lewis acids and non-reactive Br?nsted acids, which failed to perform Prins cyclization when used alone, have shown remarkable synergistic effects when used in combination to perform the reaction successfully.     

Utilization of an oxonia-Cope rearrangement as a mechanistic probe for Prins cyclizations

An oxonia-Cope rearrangement was used as an internal clock reaction to probe the mechanism of the Prins cyclization reaction and the subsequent nucleophilic capture of the resultant tetrahydropyranyl cation. The oxonia-Cope rearrangement was shown to occur rapidly under typical Prins cyclization conditions when the oxocarbenium ion resulting from the rearrangement is similar to or lower in energy than the starting oxocarbenium ion. Oxonia-Cope rearrangements can be disfavored by destabilizing the resultant oxocarbenium ion or by stabilizing an intermediate tetrahydropyranyl cation. Stereoselectivity in the nucleophilic capture was dramatically affected by the reactivity of the nucleophile and electrophile. More reactive partners combined rapidly to give axial-substituted Prins products through a least-motion pathway. High selectivity for the equatorial-substituted tetrahydropyran was observed for less reactive nucleophiles and electrophiles.     

Surfactant-type Brønsted acid catalyzed dehydrative nucleophilic substitutions of alcohols in water

A protocol for the dehydrative nucleophilic substitution of benzyl alcohols with a variety of carbon- and heteroatom-centered nucleophiles using dodecylbenzenesulfonic acid (DBSA) as a surfactant-type Br?nsted acid catalyst in water has been developed. The reaction system can be applied to the stereoselective C-glycosylation of 1-hydroxy sugars in water. [reaction: see text].     

Racemization in Prins cyclization reactions

Isotopic labeling experiments were performed to elucidate a new mechanism for racemization in Prins cyclization reactions. The loss in optical activity for these reactions was shown to occur by 2-oxonia-Cope rearrangements by way of a (Z)-oxocarbenium ion intermediate. Reaction conditions such as solvent, temperature, and the nucleophile employed played a critical role in whether an erosion in enantiomeric excess was observed. Additionally, certain structural features of Prins cyclization precursors were also shown to be important for preserving optical purity in these reactions.     

Synthesis of the C22-C26 tetrahydropyran segment of phorboxazole by a stereoselective prins cyclization

[formula: see text] Tetrahydropyran rings are found in many complex natural products, and the segment-coupling Prins cyclization is an effective strategy for their synthesis. We report a four-step, stereoselective synthesis of the C20-C27 tetrahydropyran segment of phorboxazole. The key step is a Prins cyclization induced by catalytic BF3.OEt2.     

MIL-101(Fe)高效催化 β-蒎烯与甲醛的Prins缩合制备诺卜醇

通过水热晶化法制备了MIL-101(Fe)金属有机骨架材料, 利用X射线衍射(XRD)、 傅里叶变换红外光谱(FTIR)、 热重分析(TG)、 扫描电子显微镜(SEM)、 透射电子显微镜(TEM)和X射线光电子能谱(XPS)对催化剂的结构和形貌进行了表征. 结果表明, 该材料用于催化β-蒎烯与甲醛的Prins缩合制备诺卜醇反应的效果优异; 催化剂合成温度、 合成时间、 催化剂用量、 反应溶剂、 反应温度和反应时间对β-蒎烯的反应结果均有一定影响. 在相似的反应条件下, 合成的MIL-101(Fe)催化β-蒎烯制备诺卜醇反应的最佳条件为使用150 ℃下反应15 h合成的催化剂MIL-101(Fe), 在90 ℃下反应8 h得到的β-蒎烯转化率高达97.3%, 诺卜醇选择性达到96.7%.     

Rapid stereocontrolled assembly of the fully substituted C-aryl glycoside of kendomycin with a Prins cyclization: a formal synthesis

Prins cyclization using an electron-rich benzaldehyde and a homoallylic alcohol efficiently delivered the fully substituted C-aryl tetrahydropyranoside of kendomycin.     

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.