One-Step Transformation of Tetrahydropyranyl Ethers Using Indium(III) Triflate as the Catalyst

Abstract

NotesTetrahydropyranyl (THP) group is a well-utilized moiety, mainly as a tool to protect alcohol units due to its feasibility of installation and low cost. Stirring the free alcohols with 3,4-dihydro-2H-pyran (DHP) under acidic conditions can easily produce THP-protected alcohols.1-8) Also, THP-protected alcohols are generally stable under a wide range of reaction conditions and reagents, such as metal hydrides, alkyllithiums, Grignard reagents, and catalytic hydrogenation. O, 19,20) and CuSO 4 · 5H 2 O, 21) has also been reported.Previously, we have reported a couple of convenient reaction methods using indium or indium-related reagents. [22][23][24][25] The authors have recently developed a practical approach to tetrahydropyranylation and depyranylation of various alcohols using indium(III) triflate.26) It is worth noting that with the same catalyst, the reactions proceed in directions of both protection and deprotection. In the presence of a catalytic amount of indium(III) triflate, protection of alcohols is carried out using CH 2 Cl 2 as the solvent, whereas deprotection uses MeOH/H 2 O as the solvent. Kamal et al. also reported that tetrahydropyranylation can be controlled using catalytic aluminum(III) triflate. 27) Another report has shown the cleavage of THP ethers using titanium(III) triflate in good yields.28) According to our earlier experiments, indium(III) triflate was revealed to be an efficient catalyst for the transformation of THP ethers into their corresponding acetates. In further intensive work, we have developed a useful transforming reaction of THP ethers using various anhydride moieties with indium(III) triflate as the catalyst. Herein, we report the details of this one-step transformation. Results and DiscussionTHP-protected benzyl alcohol and N-(2-hydroxyethyl)-phthalimide were used as the starting materials. First, the suitability of the catalysts was examined by reactions with acetic anhydride (Chart 1). In both cases, the reaction proceeded and produced excellent yields in a shorter time when indium(III) triflate was employed as the catalyst (Table 1, entries 1 and 3), as compared with indium(III) chloride (Table 1, entries 2 and 4). Giving the satisfactory results with indium(III) triflate, we then expanded our investigation to the other types of anhydrides. The reactions were carried out with THP-protected benzyl alcohol, N-(2-hydroxyethyl)phthalimide, and a wide range of anhydrides (Chart 2).As expected, the reactions with another aliphatic anhydride of isobutyric anhydride generated similar satisfactory results (Table 2, entries 1 and 7). In the case of benzoic anhydride, the reaction required an extended period of time, although acceptable results were obtained (Table 2, entries 2 and 8). With the exception of entry 5, these conditions were then applied to the cyclic anhydrides, and the reactions produced entirely poor yields. These results were presumably due to the low reaction temperature. When reactions were resumed at reflux using THF as the solvent, good to excellent out...

Mono(imidazolin-2-iminato) Actinide Complexes: Synthesis and Application in the Catalytic Dimerization of Aldehydes

“…After 24 h, the tube was opened to air, and the reaction was quenched with methanol. The products were identified by 1 H NMR spectroscopy and MS analysis, and the chemical shifts were compared with previously reported literature data. ,− …”

“…The cross-esterification of benzaldehyde (93.0 μL, 0.896 mmol) and isobutyraldehyde (20.0 μL, 0.224 mmol) was carried out following the general procedure described above. Benzylisobutyrate was obtained in 80% yield after a reaction time of 1.5 h. 1 H NMR (300.00 MHz, C 6 D 6 ): δ 1.17 (d, J = 7.30 Hz, 6 H, C H 3 ), 2.51–2.53 (m, 1 H, C H ), 5.10 (s, 2 H, C H 2 ), 7.25–7.38 (m, 5 H, H ar ). MS: m / z 179.17 (M + ), 73.08 (CH­(CH 3 ) 2 CO + ).…”

Chloramine-T-Mediated Oxidation of Benzylic Alcohols Using Indium(III) Triflate

“…On the other hand, we have reported useful methodologies focused on indium(III) triflate using solvents such as CH 2 Cl 2 , THF, or MeOH, and thus these outcomes in terms of solvents need not to deny the compatibility of Lewis acids and solvents. [19][20][21] The use of a 0.3 eq of indium(III) triflate was discovered to be one of the key factors for the optimal reaction condition (entries 1, 7, 8, and 9). The reaction without Lewis acid gave a yield of 37% (entry 9), and thus the presence of indium(III) triflate must contribute for smooth reactions based on the previously suggested reaction mechanism in a similar manner.…”

The Effect of Indium(III) Triflate in Oxone-Mediated Oxidative Methyl Esterification of Aldehydes

“…In recent years, we have studied the usage of trivalent indium reagents, 22,23) as well as indium metal-based reagents, [24][25][26][27] and reported the catalytic application of indium(III) triflate (In(OTf) 3 ) in the one-step chemical transformations. As part of our ongoing investigations, herein we wish to report the details of our study on the efficient oxidative methyl esterification of aldehydes using In(OTf) 3 .…”