More Like this

1. Decarbonylative ether dissection by iridium pincer complexes

   https://doi.org/10.1039/d0sc03736b  

   Yoo, Changho; Dodge, Henry M.; Farquhar, Alexandra H.; Gardner, Kristen E.; Miller, Alexander J. (November 2020, Chemical Science)

   A unique chain-rupturing transformation that converts an ether functionality into two hydrocarbyl units and carbon monoxide is reported, mediated by iridium( i ) complexes supported by aminophenylphosphinite (NCOP) pincer ligands. The decarbonylation, which involves the cleavage of one C–C bond, one C–O bond, and two C–H bonds, along with formation of two new C–H bonds, was serendipitously discovered upon dehydrochlorination of an iridium( iii ) complex containing an aza-18-crown-6 ether macrocycle. Intramolecular cleavage of macrocyclic and acyclic ethers was also found in analogous complexes featuring aza-15-crown-5 ether or bis(2-methoxyethyl)amino groups. Intermolecular decarbonylation of cyclic and linear ethers was observed when diethylaminophenylphosphinite iridium( i ) dinitrogen or norbornene complexes were employed. Mechanistic studies reveal the nature of key intermediates along a pathway involving initial iridium( i )-mediated double C–H bond activation. 

   more » « less
2. Boron insertion into alkyl ether bonds via zinc/nickel tandem catalysis

   https://doi.org/10.1126/science.abg5526  

   Lyu, Hairong; Kevlishvili, Ilia; Yu, Xuan; Liu, Peng; Dong, Guangbin (April 2021, Science)

   Mild methods to cleave the carbon-oxygen (C−O) bond in alkyl ethers could simplify chemical syntheses through the elaboration of these robust, readily available precursors. Here we report that dibromoboranes react with alkyl ethers in the presence of a nickel catalyst and zinc reductant to insert boron into the C−O bond. Subsequent reactivity can effect oxygen-to-nitrogen substitution or one-carbon homologation of cyclic ethers and more broadly streamline preparation of bioactive compounds. Mechanistic studies reveal a cleavage-then-rebound pathway via zinc/nickel tandem catalysis. 

   more » « less
3. Anti-Markovnikov terminal and gem -olefin hydrosilylation using a κ ⁴ -diimine nickel catalyst: selectivity for alkene hydrosilylation over ether C–O bond cleavage

   https://doi.org/10.1039/C8DT04608E  

   Rock, Christopher L.; Trovitch, Ryan J. (January 2019, Dalton Transactions)

   The phosphine-substituted α-diimine Ni precursor, ( Ph2PPr DI)Ni , has been found to catalyze alkene hydrosilylation in the presence of Ph 2 SiH 2 with turnover frequencies of up to 124 h −1 at 25 °C (990 h −1 at 60 °C). Moreover, the selective hydrosilylation of allylic and vinylic ethers has been demonstrated, even though ( Ph2PPr DI)Ni is known to catalyze allyl ester C–O bond hydrosilylation. At 70 °C, this catalyst has been found to mediate the hydrosilylation of ten different gem -olefins, with turnover numbers of up to 740 under neat conditions. Prior and current mechanistic observations suggest that alkene hydrosilylation takes place though a Chalk–Harrod mechanism following phosphine donor dissociation. 

   more » « less
4. General Approach to N ⁶ ,C5′-Difunctionalization of Adenosine

   https://doi.org/10.1021/acs.joc.1c01587  

   Sebastian, Dellamol; Satishkumar, Sakilam; Pradhan, Padmanava; Yang, Lijia; Lakshman, Mahesh K. (January 2022, The Journal of Organic Chemistry)

   Among the C6 halo purine ribonucleosides, the readily accessible 6-chloro derivative has been known to undergo slow SNAr reactions with amines, particularly aryl amines. In this work, we show that in 0.1 M AcOH in EtOH, aryl amines react quite efficiently at the C6 position of 2’,3’,5’-tri-O-(t-BuMe2Si)-protected 6-chloropurine riboside (6-ClP-riboside), with concomitant cleavage of the 5’-silyl group. These two-step processes proceeded in generally good yields and notably, reactions in the absence of AcOH were much slower and/or lower yielding. Corresponding reactions of 2’,3’,5’-tri-O-(t-BuMe2Si)-protected 6-ClP-riboside with alkyl amines proceeded well but without desilylation at the primary hydroxyl terminus. These differences are likely due to the acidities of the ammonium hydrochlorides formed in these reactions, and the role of AcOH was not desilylation but possibly only purine activation. With 50% aqueous TFA in THF at 0 oC, cleavage of the 5’-silyl group from 2’,3’,5’-tri-O-(t-BuMe2Si)-protected N6 alkyl adenosine derivatives and from 6-ClP-riboside was readily achieved. Reactions of the 5’-deprotected 6-ClP-riboside with alkyl amines proceeded in high yields and under mild conditions. Because these complementary methodologies yielded N6 aryl and alkyl adenosine derivatives containing a free 5’-hydroxyl group, a variety of product functionalizations was undertaken to yield N6,C5’ doubly modified nucleoside analogues. 

   more » « less
5. Ag ^I ‐Catalyzed Reaction of Enol Diazoacetates and Imino Ethers: Synthesis of Highly Functionalized Pyrroles

   https://doi.org/10.1002/anie.202101641  

   Dong, Kuiyong; Humeidi, Ahmad; Griffith, Wendell; Arman, Hadi; Xu, Xinfang; Doyle, Michael P. (May 2021, Angewandte Chemie International Edition)

   Abstract An unprecedented Ag^I‐catalyzed efficient method for the coupling of imino ethers and enol diazoacetates through a [3+2]‐cycloaddition/C−O bond cleavage/[1,5]‐proton transfer cascade process is reported. The general class of imino ethers that includes oxazolines, benzoxazoles and benzimidates are applicable substrates for these reactions that provide direct access to fully substituted pyrroles with uniformly high chemo‐ and regioselectivity. High variability in substitution at the pyrrole 2‐, 5‐ and N‐positions characterizes this methodology that also presents an entry point for further pyrrole diversification via facile modification of resulting N‐functional pyrroles. 

   more » « less