Selective monotetrahydropyranylation of symmetrical diols using P 2 O 5 /SiO 2 under solvent-free conditions and their depyranylation Hossein Eshghi * , Mohammad Rahimizadeh, Sattar Saberi Department of Chemistry, Ferdowsi University of Mashhad, Mashhad 91775-1436, Iran Received 26 February 2008 Abstract Selective protection of one of the hydroxyl group in 1, n-symmetrical diols is achieved by P 2 O 5 /SiO 2 -catalyzed reaction of the diol with dihydropyran under solvent-free conditions at room temperature. This selective protection is simple and it occurred under economically cheap conditions in high yield. The deprotected diol is simply obtained by refluxing of this compound in methanol using the same catalyst without any byproduct formation or additional purifications. # 2008 Hossein Eshghi. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Heterogeneous catalyst; P 2 O 5 /SiO 2 ; Monotetrahydropyranylation; Protecting group; Symmetrical diols The choice of the protection and deprotection strategy in a synthetic sequence is inevitable, owing to chemoselective transformations in the presence of various functional groups. 3,4-Dihydro-2H-pyran (DHP) is one of the most widely used protecting groups during a multi-step organic synthesis. The most advantages of tetrahydropyranyl (THP) ethers are: low cost and remarkable stability towards various reaction conditions such as strong bases, organometallic reagents, hydrides, redox reagents, alkylating and acylating agents, catalytic hydrogenation, and also easy removal under mild acidic conditions [1,2]. Although several reagents are available for tetrahydropyranylation of alcohols, the reported methods for monotetrahydropyranylation of symmetrical diols are very limited. Only a few recent reports have described the use of metallic sulfate supported on silica gel [3], acidic ion exchange resins [4], iodine [5], ZrO 2 -pillared clay [6], ferric sulfate hydrate [7] and ionic liquid [8] as catalyst for this purpose. However, most of these procedures suffer from one or more disadvantages such as expensive and toxic reagent, organic solvents, high temperature, stringent conditions, long reaction time, incompatibility with other acid-sensitive functional groups and needs of large amounts of catalysts. As a part of our ongoing research program to develop new synthetic methodologies [9–12] we have found that P 2 O 5 /SiO 2 can be used as a useful catalyst for selective tetrahydropyranylation of different 1,n-diols under solventless conditions as shown in Scheme 1. The depyranylation could be readily achieved using the same quantities of the catalyst in methanol under reflux conditions. www.elsevier.com/locate/cclet Available online at www.sciencedirect.com Chinese Chemical Letters 19 (2008) 1063–1067 * Corresponding author. E-mail address: heshghi@ferdowsi.um.ac.ir (H. Eshghi). 1001-8417/$ – see front matter # 2008 Hossein Eshghi. Publishedby Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2008.06.031