z Catalysis Tuning Acidity of Sulfonated Mesoporous Polymers (MP À SO 3 H) for Efficient Tetrahydropyranylation of Alcohols at Room Temperature SathyapalR. Churipard, [a,b] KempannaS. Kanakikodi, [a,b] Nileena Jose, [c] and SanjeevP. Maradur* [a] The sulfonated mesoporous polymers (MP À SO 3 H) with varying acidityweresynthesizedbytemplatefreesolvothermalmethod followed by sulfonation at different intervals of time. The catalyticactivitiesweretestedforthetetrahydropyranylationof alcohols. Among the synthesized materials, MP À SO 3 H-12 was found to be efficient and demonstrated the highest yield of pyranylated product which is superior in contrast to various heterogeneous catalysts screened. Furthermore, the substrate scope was extended to various primary, secondary, benzylic, aromatic, substituted aromatic and bulkier alcohol substrates. The catalyst retained its heterogeneity and there is no loss in its activity beyond three catalytic runs. The results observed herein are significant and comparable with the best reports available in the open literature. These interesting findings observed over MP À SO 3 H-12 make it a potential candidate for the pyranylation of various alcohols under ambient reaction conditions. 1. Introduction The utilization of protecting groups is inevitable in synthetic organic chemistry. The chemoselective transformation of a target functional group in a multifunctional molecule is a challenging task for an organic chemist but this predicament can be turned away with the help of protecting groups. [1,2] Protectionofhydroxylgroupplaysavitalroleinthemulti-step organic synthesis of complex molecules such as natural products and biologically active compounds. [3] There are more than 150 hydroxyl protecting groups reported to date, but owing to its stability and chemical compatibility with various reaction conditions, 3,4-dihydro-2H-pyran (DHP) is an attractive protecting group for the protection of alcohols. DHP is cheap, easy to synthesize and it can be easily deprotected after the reaction. [1,4] THP ethers obtained by the tetrahydropyranylation of alcohols with DHP are compatible with various reagents like alkyllithiums, metal hydrides, catalytic hydrogenation, Grignard reagents and so forth. [2] In addition, THP ethers can be transformed into wide range of useful chemicals such as halides, [5] esters, [6] sulfides, cyanides and carbonyl compounds. These benign features of DHP and extensive applications of end products obtained from the tetrahydropyranylation of alcohols have created enormous research interest in synthetic organic chemistry. [7] Most commonly, homogeneous catalysts such as p-toluenesulfonic acid (PTSA), [8] ZrCl 4 , [9] pyridinium p- toluenesulfonate (PPTS), [10] polyaniline salt, [11] NH 4 Cl, [12] etc are employedforthetetrathydropyranylationofalcohols.However, these catalytic approaches are associated with several draw- backs such as elevated reaction temperatures, prolonged reactiontimes,expensivereagentsandlackofreusability. To avoid the intrinsic shortcomings of homogeneous catalytic systems, heterogeneous catalysts are reported for the tetrahydropyranylation of alcohols. Compared to homogenous catalysts, heterogeneous catalysts offer several advantages such as easy separation, [13] good recyclability and enhanced product selectivity. ,[14,15,16] Most widely used heterogeneous catalysts include zeolites„ [17] porous silicas ,[18,19,20,21] and ion- exchange resins. [22] Recently, metal oxides, ,[23,24,25,26] MOFs [27,8,29,30] Ionic liquids [31] and porous polymers ,[32,33,34,35] are also being explored for catalytic applications. Heterogeneous catalysts such as natural clays, [36] ion-exchange resins, [22] silica-based sulfonic acid, [37] Fe 3 O 4 @SiO 2 @SO 3 H, [4] polyaniline sulfate, [11] car- bon-based solid acid, [38] SiO 2 -p-TSA, [39] zeolites [40] etc have been extensively investigated for tetrahydropyranylation of alcohols. However, many of the catalysts show lower catalytic activity except few catalysts which have shown exceptional catalytic activities. Despite the higher activity, these catalysts require severe reaction conditions or higher catalyst amount which makes the overall process expensive. Therefore it is more desirable to develop heterogeneous catalysts for the highly efficient conversion of alcohols to tetrahydropyranyl ethers undermilderreactionconditions. In this context, mesoporous polymers are the potential candidates to be used for tetrahydropyranylation of alcohols [a] S. R. Churipard, K. S. Kanakikodi, Dr. S. P. Maradur Materials Science Division, Poornaprajna Institute of Scientific, Research (PPISR), Bidalur Post, Devanahalli, Bangalore-562164, Karnataka State, India E-mail:sanjeevpm@poornaprajna.org [b] S. R. Churipard, K. S. Kanakikodi Graduate Studies, Manipal Academy of Higher Education University, Manipal-576104,Karnataka,India [c] N. Jose St. Aloysius College, Light House Hill Road, Hampankatta, Mangaluru, 575003,Karnataka Supporting information for this article is available on the WWW under https://doi.org/10.1002/slct.201903676 Full Papers DOI: 10.1002/slct.201903676 293 ChemistrySelect 2020, 5,293–299 ©2020Wiley-VCHVerlagGmbH&Co.KGaA,Weinheim