More Like this

1. 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. 

   more » « less
2. 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. 

   more » « less
3. 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. 

   more » « less
4. 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. 

   more » « less
5. Non-Classical Amide Bond Formation: Transamidation and Amidation of Activated Amides and Esters by Selective N–C/O–C Cleavage

   https://doi.org/10.1055/s-0040-1707101  

   Li, Guangchen; Szostak, Michal (January 2020, Synthesis)

   In the past several years, tremendous advances have been made in non-classical routes for amide bond formation that involve transamidation and amidation reactions of activated amides and esters. These new methods enable the formation of extremely valuable amide bonds via transition-metal- catalyzed, transition-metal-free or metal-free pathways by exploiting chemoselective acyl C–X (X = N, O) cleavage under mild conditions. In a broadest sense, these reactions overcome the formidable challenge of activating C–N/C–O bonds of amides or esters by rationally tackling nN→π*C=O delocalization in amides and nO→π*C=O donation in esters. In this account, we summarize the recent remarkable advances in the development of new methods for the synthesis of amides with a focus on (1) transition-metal/NHC- catalyzed C–N/C–O bond activation, (2) transition-metal-free highly selective cleavage of C–N/C–O bonds, (3) the development of new acyl-transfer reagents, and (4) other emerging methods. 

   more » « less