Selective esterification of the polyphenol resveratrol at the 4′-position

Selective esterification of the polyphenol resveratrol was performed under thermodynamic conditions using NaH and acid anhydrides to directly access 4′-esters. Standard conditions with acetyl chloride and pyridine showed poor selectivity, favoring esterification at the 3-position. The extended 4′-phenolate anion is generated in preference to the 3-phenolate under the new anhydride-sodium hydride-DMSO conditions. Acylation occurs to access the 4′-ester products with modest selectivity and yield with minimal formation of the 3-monoester, 3,5-diester, and triester products.     

A novel chemical modification at the 5-position of uridine derivatives

A novel chemical modification was achieved at the 5-position of 2′,3′-O-isopropylideneuridine (6) in a one-pot procedure and a remarkable effect of the base on the progress of the reaction was found.     

Selective modification of two-dimensional MoS2 nanosheets by polymer grafting

We reported on the direct creation of polymer brushes on two-dimensional molybdenum disulfide via the formation of C-S bond by UV-induced photopolymerization. The functionalization can be manipulated in forming polymer grafts on one side or both sides of the nanosheets.     

Cyclopropylation of arylamines at the 2-position with cyclopropylmagnesium carbenoids

Direct cyclopropylation of arylamines at the 2-position with 1-chlorocyclopropyl phenyl sulfoxides was achieved. The reaction of N-lithio arylamines with cyclopropylmagnesium carbenoids, which are generated from 1-chlorocyclopropyl phenyl sulfoxides with i-PrMgCl via the sulfoxide-magnesium exchange reaction, is the key of this procedure. This method offers an unprecedented way for the synthesis of arylamines having a cyclopropane ring at the 2-position directly from arylamines.     

Lithiation and functionalization of 1-alkynylimidazoles at the 2-position

Functionalization reactions of 1-alkynylimidazoles involving the formation of their 2-lithio derivatives followed by addition of various electrophiles are presented. This allows access to previously unreported 1,2-dialkynylimidazoles via 1-alkynyl-2-iodoimidazoles. The use of an aldehyde or sulfonimine electrophiles allows the direct formation of bicyclic ring systems.     

Selective modification of glycine residues in dipeptides

Reaction of dipeptides with N-bromosuccinimide results in selective α-bromination of glycine residues. Subsequent reactions of brominated peptides with diethyl malonate and allyltributyltin afford the diethyl malonyl- and allyl-substituted glycine derivatives, respectively.     

Alkenylation of thiophenes at the 2-position with magnesium alkylidene carbenoids

Treatment of magnesium alkylidene carbenoids, generated from 1-chlorovinyl p-tolyl sulfoxides with isopropylmagnesium chloride at −78 °C in toluene, with 2-lithiothiophenes gave 2-alkenylated thiophenes in good to high yields. The intermediate of this reaction was found to be an alkenylmagnesium, which could be trapped with iodoalkanes and ethyl chloroformate. This procedure offers a novel and efficient one-pot synthesis of thiophenes having a disubstituted or a trisubstituted olefin at the 2-position from thiophenes in good yields.     

Selective modification of the acid-base properties of ceria by supported Au

Au supported on CeO(2) prepared by deposition-precipitation with urea leads to a basic catalyst. Au acts in two ways as surface modifier. First, Au selectively interacts with Ce(4+) cations by either blocking access to or reducing Ce(4+) to Ce(3+). Second, the resulting Au atoms (presumably as Au(+) ions) act as soft, weak Lewis acid sites stabilizing carbanion intermediates and enhancing hydride abstraction in the dehydrogenation of alcohols. In consequence, the thus-synthesized basic catalyst catalyzes the dehydrogenation of propan-2-ol to acetone with high efficiency and without notable deactivation. Additionally, the dehydration pathway of propan-2-ol is eliminated, as Au also quantitatively blocks access to strongly acidic Ce(4+) ions or reduces them to Ce(3+).     

Rerouting nucleophilic substitution from the 4-position to the 2- or 6-position of 2,4-dihalopyridines and 2,4,6-trihalopyridines: the solution to a long-standing problem

2,4-Difluoro-, 2,4,6-trifluoro-, and 2,3,4,6-tetrafluoropyridine undergo nucleophilic substitution preferentially if not exclusively at the 4-position. However, after the introduction of a trialkylsilyl group at C-3 or C-5, the halogen at the 6-(2-)position is displaced selectively. This synthetically valuable regiocontrol can also be realized with other halopyridines such as 2,4-dichloro- and 2,4,6-trichloropyridine.     

Catalytic enantioselective Friedel-Crafts alkylation at the 2-position of indole with simple enones

A procedure for the enantioselective alkylation of indole at the 2-position with simple non-chelating enones is described for the first time. Reaction between 4,7-dihydroindole and enones in the presence of zirconium(IV)-BINOL complexes, followed by a p-benzoquinone oxidation gives indoles alkylated at the 2-position with good yields and moderate enantioselectivities.     

Intramolecular nucleophilic cyclization of 3-substituted pyridylalkylamines onto the 2-position of the pyridine ring

The intramolecular nucleophilic cyclization of 4-(3-pyridyl)butylamine ( 4a ) to yield 6,7,8,9-tetrahydro-5H-pyrido[2,3-b]azepine ( 5 ) was investigated. Of eleven different alkali metal reagents sodium, sodium hydride, sodium amide, and potassium hydride gave good yields of 5 . The sodium conditions when applied to 3-(3-pyridyl)propylamine ( 4b ) afforded 1,2,3,4-tetrahydro-1,8-naphthyridine ( 6 ) in good yield.     

The 2-position of imidazolium ionic liquids: substitution and exchange

The 2-position of imidazolium cations is known to be relatively acidic, leading to the useful Arduengo-type carbenes. At the same time, the acidity of this site can lead to undesired side reactions when using imidazolium-based ionic liquids as solvents. In this note, we describe the surprisingly facile deuterium exchange at this position and also the synthesis and exchange under modestly basic conditions (triethylamine) of a series of 2-methyl-substituted compounds.     

Ir-catalyzed functionalization of 2-substituted indoles at the 7-position: nitrogen-directed aromatic borylation

Ir-catalyzed borylation of 2-substituted indoles selectively yields 7-borylated products in good yields. N-Protection, required for previous functionalizations of 2-substituted indoles, is unnecessary.     

Selective tryptophan modification with rhodium carbenoids in aqueous solution

A new transition metal-based reaction has been developed for the selective modification of tryptophan residues on protein substrates. After activation of vinyl-substituted diazo compounds by Rh2(OAc)4, the resulting metallocarbenoid intermediates were found to modify indoles in aqueous media despite competing reactions with water. Both N- and 2-substituted indole products were observed in the reaction. Following initial small-molecule studies, the reaction was performed on two protein substrates. Both myoglobin and subtilisin Carlsberg were modified readily in aqueous solution, and the tryptophan selectivity of the reactions was confirmed through MS analyses of trypsin digest fragments. It was also demonstrated that myoblobin concentrations as low as 10 muM still led to appreciable levels of modification. Reconstitution experiments confirmed that myoglobin retained its ability to bind heme following modification.