Simple and efficient chemoselective mild deprotection of acetals and ketals using cerium(III) triflate

A new and chemoselective method for the cleavage of alkyl and cyclic acetals and ketals at room temperature in wet nitromethane by using catalytic cerium(III) trifluoromethane sulfonate is presented. The high yields, the observed selectivity, the very gentle reaction conditions, and the almost neutral pH make this procedure particularly attractive for multistep synthesis.     

Mild and chemoselective catalytic deprotection of ketals and acetals using cerium(IV) ammonium nitrate

Cerium(IV) ammonium nitrate (CAN) is a powerful, though mild, reagent for the efficient and selective removal of a range of ketals and acetals. This novel deprotection method requires only catalytic amounts of CAN and tolerates a variety of functional and protecting groups. Mechanistic insights suggest that the Ce(IV) salts act as unique Lewis acids and not as redox active species.     

A simple and versatile method for the synthesis of acetals from aldehydes and ketones using bismuth triflate

Acetals are obtained in good yields by treatment of aldehydes and ketones with trialkyl orthoformate and the corresponding alcohol in the presence of 0.1 mol % Bi(OTf)3.4H2O. A simple procedure for the formation of acetals of diaryl ketones has also been developed. The conversion of carbonyl compounds to the corresponding 1,3-dioxolane using ethylene glycol is also catalyzed by Bi(OTf)3.4H2O (1 mol %). Two methods, both of which avoid the use of benzene, have been developed.     

An efficient and chemoselective deprotection of aryl- and styrenyldithioketals (acetals)

In this Letter, an efficient and chemoselective deprotection of aryl- and styrenyldithioketals (acetals) is described. After being carefully examined, 10% Pd/C and Amberlite 120 in refluxing methanol was found to be an excellent condition for the chemoselective deprotection of aryl- and styrenyldithioketals (acetals) in good yields. Under this condition, no deprotection and no reduction of alkyldithioketals (acetals) was observed.     

Indium(III) trifluoromethanesulfonate as an efficient catalyst for the deprotection of acetals and ketals

Acetals and ketals are readily deprotected under neutral conditions in the presence of acetone and catalytic amounts of indium(III) trifluoromethanesulfonate (<0.8 mol %) at room temperature or mild microwave heating conditions to give the corresponding aldehydes and ketones in good to excellent yields.     

Mild and efficient method for the cleavage of benzylidene acetals by using erbium (III) triflate

Er(OTf)3 is proposed as new efficient Lewis acid catalyst in a mild deprotection protocol of benzylidene derivatives. In a modified procedure, where acetic anhydride is used as the reaction solvent, the simultaneous cleavage of the benzylidene acetal and the peracetylation of the substrates is obtained in quantitative yields and very short reaction times.     

A simple deprotection of triflate esters of phenol derivatives

Efficient conversion of aryl triflates into the corresponding phenols has been accomplished with Et₄NOH. In contrast to other cleavage reactions, such functional groups as nitro, ketone, halogen, amide and sulfonamide groups were intact under the reaction conditions. This mild removal of the trifluoromethanesulfonyl group would serve a new protecting group of phenols.     

The chemoselective and efficient deprotection of silyl ethers using trimethylsilyl bromide

An efficient and chemoselective cleavage of silyl ethers (primary, secondary and aromatic) by using catalytic quantities of trimethylsilyl bromide (TMSBr) in methanol is reported. A wide range of alkyl silyl ethers such as TBS, TIPS, and TBDPS can be chemoselectively cleaved in high yield in the presence of aryl silyl ethers. The deprotection of silyl esters was also achieved employing catalytic quantities of TMSBr.     

Environment friendly organic synthesis using bismuth compounds. An efficient method for carbonyl-ene reactions catalyzed by bismuth triflate

Bismuth triflate (0.1 mol %) is a highly efficient catalyst for the cyclization of citronellal 1, a reaction that yields a ratio of 80:20 of isopulegol 2 and neoisopulegol 3. This methodology has also been extended to the synthesis of substituted piperidines. The bismuth triflate catalyzed ene reaction of aldehyde 4 gives a 70:30 mixture of piperidines 5 and 6. The advantages of these methods include the use of a highly efficient catalyst that is relatively nontoxic, cheap and easy to handle.     

Zinc triflate: A mild and efficient catalyst for deprotection of tetrahydropyranyl ethers

Treatment of tetrahydropyranyl (THP) ethers with zinc triflate in methanol provides a simple and efficient process for deprotection of these ethers and the parent alcohols are obtained in excellent yields.     

A mild and efficient method for the chemoselective deprotection of acetonides with lanthanum(III) nitrate hexahydrate

Acetonides are hydrolyzed selectively and efficiently with lanthanum(III) nitrate hexahydrate in acetonitrile. The method has good compatibility with other sensitive hydroxyl protecting groups such as trityl, TBDMS, THP, OAc, OBz and OBn.     

An efficient catalytic deprotection of thioacetals employing bismuth triflate: synthesis of pyrrolo[2,1-c] [1,4] benzodiazepines

A simple and efficient deprotection of thioacetals has been achieved by employing bismuth triflate. This method has been effectively employed in the preparation of DNA-binding pyrrolo[2,1-c] [1,4]benzodiazepine and its dimers.     

Efficient chemoselective deprotection of silyl ethers using catalytic 1-chloroethyl chloroformate in methanol

Fast and chemoselective desilylation of silyl-protected alcohols was achieved using a catalytic amount of 1-chloroethyl chloroformate in methanol. With a minimal amount of 1-chloroethyl chloroformate as the source for anhydrous HCl, extremely efficient cleavage of silyl ethers of primary and secondary alcohols was accomplished, and chemoselective deprotection of one silyl ether in the presence of another silyl or other acid-labile group was possible through controlling the amount of the chloroformate and reaction time.     

CpRuIIPF6/quinaldic acid-catalyzed chemoselective allyl ether cleavage. A simple and practical method for hydroxyl deprotection

A cationic CpRu(II) complex in combination with quinaldic acid shows high reactivity and chemoselectivity for the catalytic deprotection of hydroxyl groups protected as allyl ethers. The catalyst operates in alcoholic solvents without the need for any additional nucleophiles, satisfying the practical requirements of operational simplicity, safety, and environmental friendliness. The wide applicability of this deprotection strategy to a variety of multifunctional molecules, including peptides and nucleosides, may provide new opportunities in protective group chemistry. [structure: see text]     

Highly efficient deprotection of aromatic acetals under neutral conditions using beta-cyclodextrin in water

Aromatic acetals have been deprotected to the corresponding aldehydes under biomimetic conditions for the first time using beta-cyclodextrin in water under neutral conditions, thereby overcoming many of the drawbacks associated with earlier methodologies. This method, apart from being simple with regard to recycling of the catalyst, also has the potential for industrial applications.     

Environmentally friendly organic synthesis using bismuth compounds: bismuth(III) iodide catalyzed deprotection of acetals in water

The chemoselective deprotection of a wide range of acetals and ketals in water is catalyzed by bismuth(III) iodide. Bismuth(III) compounds are remarkably nontoxic and hence are attractive as environmentally friendly catalysts.     

Pd(II)-catalyzed deprotection of acetals and ketals containing acid sensitive functional groups

The pincer complex [Pd(C¹,O¹,N¹-L)(NCMe)]ClO₄ (L = monoanionic ligand resulting from deprotonation of the acetyl group of the dimethyl monoketal of 2,6-diacetylpyridine) is used for the high-yield and selective catalytic hydrolysis of aliphatic, aromatic, cyclic, and acyclic dimethyl-acetals, -ketals, and dioxolanes, even in the presence of large substituents. Other protecting groups, such as THP or TBDMS, or very acid-sensitive alcohols were not affected. The catalyst is easily prepared in high yield from Pd(AcO)₂ and 2,6-diacetylpyridinium perchlorate stable to air and moisture, easily and fully recoverable and reusable.     

A simple method for chemoselective phenol alkylation

A simple and effective method for chemoselective alkylation of phenol over carboxylic acid using a 40% aqueous solution of tetrabutylphosphonium hydroxide that affords the desired phenyl ethers in 82-99% yield is described.