A Highly Efficient and Chemoselective Synthetic Protocol for Tetrahydropyranylation/Depyranylation of Alcohols and Phenols

Abstract

Various alcohols and phenols can be converted efficiently to the corresponding tetrahydropyranyl (THP) ethers in good yields using catalytic amounts of bromodimethylsulfonium bromide (0.005−0.02 equivalent) at room temperature. On the other hand, various THP ethers can also be deprotected to the parent alcoholic or phenolic compounds in CH2Cl2/MeOH (5:2) by employing 0.05 equivalent of the same catalyst. Some of the major advantages of this procedure are its mild conditions, that it is highly selective and efficient, high yielding, and cost‐effective, that it needs no solvent and is compatible with the presence of other protecting groups. Furthermore, no brominations occur at a double or triple bond, at an allylic position or even at an aromatic ring. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Chemoenzymatic Synthesis of 3′‐O‐Acetal‐Protected 2′‐Deoxynucleosides as Building Blocks for Nucleic Acid Chemistry

“…Some reagents recently used for acetal protection are SO 3 Hfunctionalized silica, [8] polystyrene-supported AlCl 3 , [9] bromodimethylsulfonium bromide, [10] magnesium halides, [11] bismuth triflate, [12] or ruthenium trichloride. [13] The use of the THF group is less prolific due to the limited protocols available in the literature.…”

Tetrahydropyranylation of Alcohols over Modified Zeolites

“…Tetrahydropyranylation of alcohols can be accompanied by using PTSA [3], BF 3 ÁOEt 2 [4], PPTS [5] and zeolites [6][7][8][9]. Some of the recently used reagents that can catalyze tetrahydropyranylation are AlCl 3 Á6H 2 O [10], [11], Fe 2 (SO 4 ) 3 ÁXH 2 O [12], ferric perchlorate [13], Ru(acac) 3 [14], La(NO 4 ) 3 Á6H 2 O [15], 2,4,6-Trichloro [1,3,5] triazine [16], TBATB [17], In(OTf) 3 [18], InCl 3 immobilized on ionic liquids [19], bromodimethylsulfonium bromide [20], tetrabutylammonium bromide [17], CeCl 3 Á7H 2 O-NaI [21], PdCl 2 (CH 3 CN) 2 [22]. On the other hand, many methods have also been developed using heterogeneous catalysts and these have been reviewed recently [23].…”

Silica supported perchloric acid (HClO4-SiO2): A highly efficient and reusable catalyst for geminal diacylation of aldehydes under solvent-free conditions

“…From our recent result [26] as well as from the other results [27,28], we realized that perchloric acid adsorbed on silica gel has higher catalytic activity than most of the moisture sensitive and highly costly metal triflates. As a part of our ongoing research project to develop new synthetic methodologies particularly in protection and deprotection chemistry [29], we perceived that silica supported perchloric acid (HClO 4 -SiO 2 ) might be a useful, effective, versatile and reusable catalyst for chemoselective protection of aldehydes as acylals. So far, silica supported perchloric acid (HClO 4 -SiO 2 ) has been utilized mainly as catalyst for acetylation of phenols, thiols, alcohols and amines [27], peracetylation of carbohydrates [30], acetalization followed by acetylation [31] and Ferrier rearrangement of glucals [28].…”