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1. Transition Metal‐Free Aroylation of Diarylmethanes with N ‐Bn‐ N ‐Boc Arylamides and N ‐Acylpyrroles

   https://doi.org/10.1002/adsc.202000622  

   Yang, Fan; Zou, Dong; Chen, Shuguang; Wang, Huan; Zhao, Yichen; Zhao, Liyi; Li, Linlin; Li, Jie; Walsh, Patrick_J (July 2020, Advanced Synthesis & Catalysis)

   Abstract In the last 20 years, efficient transition metal catalysts for the α‐arylation of enolates have been introduced. Despite the popularity and utility of these reactions, there remains room for improvement (reduced costs, elimination of transition metals and specialized ligands). Herein is reported a general, scalable and green method for aroylation of simple diarylmethane pronucleophiles through direct acyl C−N cleavage ofN‐Bn−N‐Boc arylamides andN‐acylpyrroles under transition metal‐free conditions. Importantly, a 1 : 1 ratio of the amide to the pronucleophile is employed. Unlike use of Weinreb amides, this method avoids preformed organometallics (organolithium and Grignard reagents) and does not employ cryogenic temperatures, which are difficult and costly to achieve on scale. The operationally simple protocol provides straightforward access to a variety of sterically and electronically diverse 1,2,2‐triarylethanones, a group of compounds with high‐value in medicinal chemistry. magnified image 

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2. Chemoselective acylation of N -acylglutarimides with N -acylpyrroles and aryl esters under transition-metal-free conditions

   https://doi.org/10.1039/D1QO00992C  

   Li, Jie; Yao, Jiaqi; Chen, Lingfeng; Zou, Dong; Walsh, Patrick J.; Liang, Guang (November 2021, Organic Chemistry Frontiers)

   The imide moiety is a well-known structural motif in bioactive compounds and a useful building block in a variety of processes. Using N -acylglutarimides with MN(SiMe 3 ) 2 and either N -acylpyrroles or aryl esters, an operationally convenient method to produce a wide array of diaryl- and alkyl arylimides is presented. Symmetric imides are also accessible when N -acylglutarimides are employed as acylation reagents under similar reaction conditions. A unique feature of this method stems from the use of two different electrophilic acylating reagents leading to the formation of the unsymmetrical imides with excellent chemoselectivity. 

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3. Synthesis of N ‐Substituted Maleimides and Poly(styrene‐ co ‐ N ‐maleimide) Copolymers and Their Potential Application as Photoresists

   https://doi.org/10.1002/macp.202200256  

   Eken, Gozde_Aktas; Käfer, Florian; Yuan, Chenyun; Andrade, Ivan; Ober, Christopher_K (September 2022, Macromolecular Chemistry and Physics)

   Abstract Poly(styrene‐co‐N‐maleimide) copolymers bearingtert‐butoxycarbonyl (t‐BOC)‐protected amine groups attached to side chains of varying lengths are synthesized via activators regenerated by electron transfer atom transfer radical polymerization (ARGET‐ATRP) and investigated from the perspective of photoresist applications. The length of the alkyl substituents enables control of thermal properties as well as hydrophobicity, which are critically important for resist processing. Removal of the acid labilet‐BOC group during deep‐UV (DUV)exposure shifts solubility in the exposed areas and well‐defined line space patterns of 1 µm are obtained for the selected copolymers. The correlation between glass transition temperature (T_g) and solubility contrast determines the lithographic performance where the copolymers with shorter alkyl chains exhibit promising results. 

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4. Unnatural Lysines with Reduced Sidechain N ‐Basicity: Synthesis of N ‐trifluoroethyl Substituted Lysine and Homologs

   https://doi.org/10.1002/slct.202203132  

   Jameson, Brian; Glaser, Rainer (December 2022, ChemistrySelect)

   Abstract The syntheses are reported of N^ϵ‐(2,2,2‐trifluoroethyl)‐D,L‐lysine (^tFK) and N^ζ‐(2,2,2‐trifluoroethyl)‐D,L‐homolysine (^tFK₊₁) from amino alcohols HO−(CH₂)_n−NH₂. The syntheses involve reductive amination, Appel bromination, and the stereoselective bond formation between C_α of the amino acid and the fluorinated alkyl chain in the Schöllkopf bislactim amino acid synthesis. The methyl esters of the fluorinated amino acids are the relevant substrates for oligopeptide synthesis. With theR‐Schöllkopf reagent, we stereoselectively generated methyl N^ϵ‐boc‐N^ϵ‐(2,2,2‐trifluoroethyl)‐L‐lysinate and methyl N^ζ‐boc‐N^ζ‐(2,2,2‐trifluoroethyl)‐L‐homolysinate. Products and intermediates were characterized by ¹H NMR, ¹³C NMR, COSY, HSQC, and LCMS. A variety of N‐functionality may be introduced by reacting hemiacetals with different appendages. This fluorine modification reduces the sidechain N‐basicity by combined ‐I effect of the three fluorines. This effect increases the [amine]/[ammonium ion] ratio of the sidechain amine in lysine to facilitate carbamylation at lower pH conditions. 

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5. Transamidation of Amides and Amidation of Esters by Selective N–C(O)/O–C(O) Cleavage Mediated by Air- and Moisture-Stable Half-Sandwich Nickel(II)–NHC Complexes

   https://doi.org/10.3390/molecules26010188  

   Buchspies, Jonathan; Rahman, Md. Mahbubur; Szostak, Michal (January 2021, Molecules)

   null (Ed.)

   The formation of amide bonds represents one of the most fundamental processes in organic synthesis. Transition-metal-catalyzed activation of acyclic twisted amides has emerged as an increasingly powerful platform in synthesis. Herein, we report the transamidation of N-activated twisted amides by selective N–C(O) cleavage mediated by air- and moisture-stable half-sandwich Ni(II)–NHC (NHC = N-heterocyclic carbenes) complexes. We demonstrate that the readily available cyclopentadienyl complex, [CpNi(IPr)Cl] (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), promotes highly selective transamidation of the N–C(O) bond in twisted N-Boc amides with non-nucleophilic anilines. The reaction provides access to secondary anilides via the non-conventional amide bond-forming pathway. Furthermore, the amidation of activated phenolic and unactivated methyl esters mediated by [CpNi(IPr)Cl] is reported. This study sets the stage for the broad utilization of well-defined, air- and moisture-stable Ni(II)–NHC complexes in catalytic amide bond-forming protocols by unconventional C(acyl)–N and C(acyl)–O bond cleavage reactions. 

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