Selective Deprotection of tert -Butyldimethylsilyl Ethers Using Nafion-H®/Sodium Iodide (or Bromodimethylsulfonium Bromide) in Methanol

Abstract

Catalytic amounts of bromodimethyl sulfonium bromide, or Nafion-H along with NaI (1 equiv.), in methanol cleave a variety of TBDMS ethers readily in high yields. Alkyl TBDMS ethers react more readily and selectively compared to phenolic TBDMS ethers, benzyl, and methyl ethers.     

Preparation and Characterization of 2,2′-Dipicolyl Diselenide and Their Derivatives

Lithium 2-picolylselenolate/tellurolate is obtained by reacting lithiated 2-picoline with elemental selenium/tellurium which upon aerial oxidation gives 2,2'-dipicolyl diselenide in case of selenium while 1,2-bis(2-pyridyl)ethane in case of tellurium. Condensation of 2-picolylselenolate anion with a variety of electrophiles provides a facile synthesis of 2-picolylalkyl selenides in good to excellent yields. Quenching of lithiated 2-picoline with 2,2'-dipyridyl diselenide gives mixed 2-picolylseleno pyridine in low yield. All the compounds prepared are new and have been characterized by elemental analysis, 1 H NMR, 13 C NMR and mass spectral studies.     

CARO'S ACID SUPPORTED ON SILICA GEL,PART VIII: AN EFFICIENT AND SELECTIVE REAGENT FOR CONVERSION OF PHENYLHYDRAZONES AND SEMICARBAZONES TO THE CORRESPONDING CARBONYL COMPOUNDS

Deprotection of phenylhydrazones and semicarbazones to their parent aldehydes and ketones in high yields has been carried out using caro's acid supported on silica gel as a selective oxidant under mild conditions.     

Mn(OAc)3—an efficient oxidant for regeneration of DDQ: deprotection of p-methoxy benzyl ethers

Mn(OAc)₃ has been successfully developed as a new oxidant for the regeneration of DDQ from HDDQ. This DDQ regeneration technique, making use of 3 equiv. of Mn(OAc)₃–DDQ (10 mol%), was applied to the deprotection of p-methoxy benzyl (PMB) ethers.     

Preparation of 2-deoxystreptamine derivatives with all-axial substituents for desymmetrization

2-Deoxystreptamine derivatives with all-axial substituents were prepared with new methods. They are potential compounds for desymmetrization.     

Aqueous phosphoric acid as a mild reagent for deprotection of the t-butoxycarbonyl group

Aqueous phosphoric acid (85 wt%) is an efficient and mild reagent for the deprotection of N-BOC groups. Acid sensitive functionalities including benzyl and methyl esters, TBDMS ether, CBZ and isopropylidene groups are compatible with the reaction conditions. The reactions are high yielding, and the workup is convenient.     

Efficient regeneration of aldehydes from their corresponding 1,3-oxathiolanes in the absence of solvent

A mild and efficient method for the oxidative deprotection of 1,3-oxathiolanes with Fe（NO₃）₃·9H₂O and Cu（NO₃）₂·3H₂O in the absence of solvent is reported.     

Manipulating morphology and orientation in thermally responsive block copolymer thin films

We demonstrate the use of combined thermal annealing and solvent vapor annealing (SVA) to tune the morphology of thermally responsive block copolymer (BCP) thin films. The BCP, poly(styrene‐b‐tert‐butyl acrylate) (PS‐b‐PtBA), undergoes a chemical deprotection to poly(styrene‐b‐acrylic anhydride) (PS‐b‐PAH) above a temperature threshold, giving rise to a structural and morphological transition. Our experiments systematically examine different thermal annealing and SVA protocols with two solvents (tetrahydrofuran and acetone) and map the resulting morphologies. Assessments of these processing protocols were accelerated using temperature gradients. Our results demonstrate that the final nanoscale morphologies after SVA are determined by the changes in the relative solvent/polymer interactions and surface tensions of the polymer blocks that accompany deprotection. Because of these driving forces, certain processing combinations led to irreversible morphological states, whereas others present opportunities for further manipulation. Accordingly, our study reveals that the morphology of this thermally sensitive BCP can be altered through judicious choice of annealing protocol. The protocols that combine equal numbers of SVA and thermal annealing (TA) steps are not necessarily equivalent, and the order of the SVA relative to TA is a deciding factor in the final morphology. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Synthesis of hydroxyl‐bearing polyurethanes from naturally occurring myo‐inositol

A route from naturally occurring myo‐inositol to hydroxyl‐bearing polyurethanes has been developed. The diol prepared from the bis‐acetalization of myo‐inositol with 1,1‐dimethoxycyclohexane was reacted with a rigid diisocyanate, 1,3‐bis(isocyanatomethyl)cyclohexane to afford the corresponding polyurethane, of which glass transition temperature (T_g) was quite high as 192 °C. The polyurethane contains side chains inherited from the acetal moieties of the diol monomer and was treated with trifluoroacetic acid to hydrolyze the acetal moieties and afford the target polyurethane functionalized with hydroxyl groups. The presence of many hydroxyl groups in the side chains, which can form hydrogen bonds with each other, resulted in a high T_g, 186 °C. In addition, the hydroxyl groups were reacted with isocyanates to achieve further side‐chain modifications. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1358–1364     

Mild acetal cleavage using B-chlorocatecholborane in the synthesis of rearrangement-sensitive 2-arachidonoylglycerol

A mild method for the cleavage of an acetal to afford a rearrangement sensitive diol using B-chlorocatecholborane was developed for the synthesis of the endogenous cannabinoid neurochemical messenger 2-arachidonoylglycerol. The tendency for rearrangement of 2-arachidonoylglycerol to the corresponding 1-arachidonoylglycerol was precluded with this reagent. Features of the partial recyclization to an isomeric acetal provide mechanistic detail.