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.     

1,3-Dibromo-5,5-dimethylhydantoin (DBH) as a Mild and Efficient Catalyst for Chemoselective Thioacetalization of Carbonyl Compounds and Dethioacetalization Under Mild Conditions

Hydantoin bromide is an effective catalyst for chemoselective thioacetalization of aldehydes in the presence of ketones under neutral conditions. In addition, a simple and efficient procedure for the deprotection of 1,3-dithianes and 1,3-dithiolanes of aromatic, aliphatic, and α,β-unsaturated aldehydes and ketones in solvent-free conditions to the corresponding parent carbonyl compounds was successfully carried out with hydantoin bromide in excellent yields.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

A tandem C-H insertion—acetal cleavage sequence: stereocontrolled synthesis of substituted tetrahydrofurans

A short sequence involving Rh(II) mediated carbene insertion followed by Lewis acid promoted reductive acetal cleavage with Et₃SiH provides a stereoselective method for the construction of 2,3,5-trisubstituted tetrahydrofuran rings.     

Short communication the preparation of stable protected 3-ethynylpyrrole suitable for electrochemical polymerization

Stable protected 3-triisopropylsilylethynylpyrrole, 4b , was prepared in the yield 73% by first observed selective deprotection of double protected 1-triisopropylsilyl-3-triisopropylsilylethynylpyrrole, 3b , which was obtained in the yield 44%. This deprotection in preference proceeds at the pyrrole nitrogen leaving the 3-triisopropylsilylethynyl group intact. Due to its stability, ethynylpyrrole derivative 4b protected was like the first alkynyl pyrrole derivative electrochemically polymerized giving a black polypyrrole layer deposited on the platinum anode. Copyright © 2003 John Wiley & Sons, Ltd.     

Selectivity in the electrochemical deprotection of cinnamyl groups from oxygen and nitrogen functionalities: carbonates versus carbamates

Several cinnamyloxy carbamates and carbonates were subjected to electrochemical reduction, and the reductive fate of the cinnamyl group was investigated. Complete selectivity was observed in the removal of the cinnamyl group from oxygen versus nitrogen.     

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.     

IMMEDIATE AND HIGH YIELDING SOLVENT-FREE OXIDATION OF SILYL AND PYRANYL ETHERS TO THEIR CORRESPOUNDING CARBONYL COMPOUNDS WITH ZINC DICHROMATE TRIHYDRATE (ZnCr2O7·3H2O)

Zinc dichromate trihydrate (ZnCr₂O₇·3H₂O) is an efficient reagent for the immediate deprotection of aromatic and aliphatic silyl and pyranyl ethers into their corresponding carbonyl compounds in high yields at room temperature under solvent-free conditions.     

Mechanical,thermal, and morphological properties of powder coating waste reinforced acetal copolymer

The present study investigates the individual effects of three different thermosetting waste materials, used as fillers, on the mechanical, thermal and flow properties of acetal copolymers (POM). Different amounts ranging from 5% to 30% by weight of hydrolyzed powder coating recyclates were mixed as filler material in POM. The matrix and the fillers were first dry-mixed and then compounds were prepared through melt extrusion. The resulting compounds were cooled, granulated, and then standard tensile test bars were produced through use of an injection-molding machine. We investigated the mechanical and thermal properties of test specimens, and tensile strength, bending strength and impact strength were evaluated as a function of type and amount of filler material in the POM matrix. In addition, the change in melt flow index of POM/filler mixtures was determined, before and after extrusion. Furthermore, the morphology of the specimens was examined via electron microscopy. The results of this investigation are encouraging and present an innovative approach to reutilize hydrolyzed electrostatic powder coating wastes with thermoset structures as fillers in acetal copolymers.     

Synthesis of Novel Cryptates Based on Triazole Motif: A Regioselective Approach

Regioselective syntheses of cryptands were achieved via two different approaches, first by protection–deprotection and second by cyclization reactions between 1,ω-dihaloalkanes and the lariat amino triazolophanes. The syntheses of all triazolophanes and cryptands were carried out regioselectively, and the compounds were obtained in good yields. All compounds were studied and confirmed with different spectroscopic tools.

Simple and Highly Efficient Method for the Deprotection of Allyl Ethers Using Dimethylsulfoxide–Sodium Iodide

A simple and highly efficient method for deprotection of allyl ethers has been developed using dimethylsulfoxide–sodium iodide (catalytic amount). This method is inexpensive, has simple reaction conditions, has an easy workup procedure, proceduces excellent yields (60–99%), and is effective for several structurally varied allyl ethers.