Synthesis of novel 1,4 naphthoquinone-based molecules by an Ugi-type four-component reaction

In an attempt to further exploit multicomponent reactions in the field of 1,4 naphthoquinone-based compounds, we describe an Ugi-type multicomponent approach for the synthesis of novel 3-substituted 1,4 naphthoquinone molecules. The process relies on the execution of an enol-Ugi reaction between an enol-3-nitro-1,4 naphthoquinone with different secondary diamines and isocyanides. The novel methodology showed great chemical efficiency and versatility.     

Tantalum isocyanide complexes: TaI(CNDipp)6 (Dipp is 2,6‐diisopropylphenyl) and ionic [Ta(CNDipp)7][Ta(CNDipp)6], a formal disproportionation product of the 17‐electron Ta0 metalloradical Ta(CNDipp)6

Treatment of tetraethylammonium hexacarbonyltantalate, [Et₄N][Ta(CO)₆], with 1.1 equivalents of molecular iodine (I₂) in tetrahydrofuran (THF) at 200 K, followed by the addition of 6.0 equivalents of 2,6‐diisopropylphenyl isocyanide (CNDipp) and slow warming to 293 K over a 24 h period gave the tantalum(I) iodide derivative hexakis(2,6‐diisopropylphenyl isocyanide‐κC)iodidotantalum(I), [TaI(C₁₃H₁₇N)₆] or TaI(CNDipp)₆, 1 . Recrystallization of this substance from pentane provided deep‐red nearly black parallelepipeds of the product, which was characterized by single‐crystal X‐ray diffraction. Addition of 1 in THF at 200 K to a suspension of an excess (5.8 equivalents) of caesium graphite (CsC₈), followed by warming, filtration, and solvent removal, afforded a dark‐green oily solid of unknown composition, from which several red–brown rhombohedral plates of the ditantalum salt heptakis(2,6‐diisopropylphenyl isocyanide‐κC)tantalum hexakis(2,6‐diisopropylphenyl isocyanide‐κC)tantalate, [Ta(C₁₃H₁₇N)₇][Ta(C₁₃H₁₇N)₆] or [Ta(CNDipp)₇][Ta(CNDipp)₆], 2 , were harvested. Salt 2 is a unique substance, as it is the only known example of a salt containing a homoleptic cation, [ML_x]⁺, and a homoleptic anion, [ML_y]^?, with the same transition metal and π‐acceptor ligand L. In solution, 2 undergoes full comproportionation to afford the recently reported 17‐electron paramagnetic zerovalent tantalum complex Ta(CNDipp)₆, the only known isolable TaL₆ complex of Ta⁰.     

One-Pot Palladium-Catalyzed Ligand- and Metal-Oxidant-Free Aerobic Oxidative Isocyanide Insertion Leading to 2-Amino-substituted-4(3H)-quinazolinones

An efficient, ligand- and metal-oxidant-free, one-pot, cascade aerobic oxidative, palladium-catalyzed, multicomponent reaction has been developed through isocyanide insertion of less active secondary amide and aromatic amine, which leads to 2-amino-substituted-4(3H)-quinazolinones. This approach proves to be one of the simplest methods for the synthesis of this class of valuable bioactive heterocyclic scaffolds.     

Metal–organic framework of amine‐MIL‐53(Al) as active and reusable liquid‐phase reaction inductor for multicomponent condensation of Ugi‐type reactions

Metal–organic framework of NH₂‐MIL‐53(Al), with coordinative unsaturated aluminium sites, has been shown to be active in the Groebke–Blackburn–Bienaymé multicomponent coupling reaction based on Ugi‐type amine and aldehyde condensation over isocyanide and then a cyclization process. Interestingly this reaction occurred under solvent‐free conditions with high yield, in which the NH₂‐MIL‐53(Al) could be recovered and reused for five reaction cycles, giving a total turnover number of 455.     

Polypeptide‐b‐Poly(Phenyl Isocyanide) Hybrid Rod‐Rod Copolymers: One‐Pot Synthesis,Self‐Assembly,and Cell Imaging

Hybrid rod‐rod diblock copolymers, poly(γ‐benzyl L‐glutamate)‐poly(4‐cyano‐benzoic acid 2‐isopropyl‐5‐methyl‐cyclohexyl ester) (PBLG‐PPI), with determined chirality are facilely synthesized through sequential copolymerization of γ‐benzyl‐L‐glutamate N‐carboxyanhydride (BLG‐NCA) and phenyl isocyanide monomers bearing chiral menthyl pendants using a Ni(cod)(bpy) complex as the catalyst in one‐pot. Circular dichroism and absorption spectra reveal that each block of the block copolymers possesses a stable helical conformation with controlled helicity in solution due to the induction of chiral pendants. The two diastereomeric polymers self‐assemble into helical nanofibrils with opposite handedness due to the different chiral induction of the L‐ and D‐menthyl pendants, confirmed by transmission electron micro­scopy (TEM). Deprotection of the benzyl groups of the PBLG segment affords biocompatible amphiphilic diblock copolymers, poly(L‐glutamic acid)‐poly(4‐cyano‐benzoic acid 2‐isopropyl‐5‐methyl‐cyclohexyl ester) (PLGA‐PPI), that can self‐assemble into well‐defined micelles by cosolvent induced aggregation. Very interestingly, a chiral rhodamine chromophores RhB(D) can be selectively encapsulated into the chiral polymeric micelles, which is efficiently internalized into living cells when directly monitored with a confocal microscope. This contribution will be useful for developing novel rod‐rod biocompatible hybrid block copolymers with a controlled helicity, and may also provide unique chiral materials for potential bio‐medical applications.

     

Construction of Helically Stacked π-Electron Systems in Poly(quinolylene-2,3-methylene) Stabilized by Intramolecular Hydrogen Bonds

π-Stacked polymers, which consist of layered π-electron systems in a polymer, can be expected to be used in molecular electronic devices. However, the construction of a stable π-stacked structure in a polymer is considerably challenging because it requires sophisticated designs and precise synthetic methods. Herein, we present a novel π-stacked architecture based on poly(quinolylene-2,3-methylene) bearing alanine derivatives as the side chain, obtained through the living cyclo-copolymerization of an o-allenylaryl isocyanide. In the resulting polymer, the neighboring quinoline rings of the main chain form a layered structure with π–π interactions, which is stabilized by intramolecular hydrogen bonds. The vicinal quinoline units form two independent helices and the whole molecule is a twisted-tape structure. This structure is established on the basis of UV/CD spectra, theoretical calculations, and atomic-force microscopy.     

Construction of Helically Stacked π‐Electron Systems in Poly(quinolylene‐2,3‐methylene) Stabilized by Intramolecular Hydrogen Bonds

π‐Stacked polymers, which consist of layered π‐electron systems in a polymer, can be expected to be used in molecular electronic devices. However, the construction of a stable π‐stacked structure in a polymer is considerably challenging because it requires sophisticated designs and precise synthetic methods. Herein, we present a novel π‐stacked architecture based on poly(quinolylene‐2,3‐methylene) bearing alanine derivatives as the side chain, obtained through the living cyclo‐copolymerization of an o‐allenylaryl isocyanide. In the resulting polymer, the neighboring quinoline rings of the main chain form a layered structure with π–π interactions, which is stabilized by intramolecular hydrogen bonds. The vicinal quinoline units form two independent helices and the whole molecule is a twisted‐tape structure. This structure is established on the basis of UV/CD spectra, theoretical calculations, and atomic‐force microscopy.     

Lutetium‐Methanediide‐Alkyl Complexes: Synthesis and Chemistry

The first four‐coordinate methanediide/alkyl lutetium complex (BODDI)Lu₂(CH₂SiMe₃)₂(μ₂‐CHSiMe₃)(THF)₂ (BODDI=ArNC(Me)CHCOCHC(Me)NAr, Ar=2,6‐iPr₂C₆H₃) ( 1 ) was synthesized by a thermolysis methodology through α‐H abstraction from a Lu–CH₂SiMe₃ group. Complex 1 reacted with equimolar 2,6‐iPrC₆H₃NH₂ and Ph₂C?O to give the corresponding lutetium bridging imido and oxo complexes (BODDI)Lu₂(CH₂SiMe₃)₂(μ₂‐N‐2,6‐iPr₂C₆H₃)(THF)₂ ( 2 ) and (BODDI)Lu₂(CH₂SiMe₃)₂(μ₂‐O)(THF)₂ ( 3 ). Treatment of 3 with Ph₂C?O (4 equiv) caused a rare insertion of Lu–μ₂‐O bond into the C?O group to afford a diphenylmethyl diolate complex 4 . Reaction of 1 with PhN=C?O (2 equiv) led to the migration of SiMe₃ to the amido nitrogen atom to give complex (BODDI)Lu₂(CH₂SiMe₃)₂‐μ‐{PhNC(O)CHC(O)NPh(SiMe₃)‐κ³N,O,O}(THF) ( 5 ). Reaction of 1 with tBuN?C formed an unprecedented product (BODDI)Lu₂(CH₂SiMe₃){μ₂‐[η²:η²‐tBuNC(=CH₂)SiMe₂CHC?NtBu‐κ¹N]}(tBuN?C)₂ ( 6 ) through a cascade reaction of N?C bond insertion, sequential cyclometalative γ‐(sp³)‐H activation, C?C bond formation, and rearrangement of the newly formed carbene intermediate. The possible mechanistic pathways between 1 , PhN?C?O, and tBuN?C were elucidated by DFT calculations.     

Efficient and Mild Protocol for the Synthesis of 4(3)-Substituted 3(4)-Nitro-1H-pyrroles and 3-Substituted 4-Methyl-2-tosyl-1 H-pyrroles from Nitroolefins and Tosylmethyl Isocyanide in Ionic Liquids

A mild and convenient method for the synthesis of 4(3)‐substituted 3(4)‐nitro‐1H‐pyrroles and 3‐substituted 4‐methyl‐2‐tosyl‐1H‐pyrroles from nitroolefins and tosylmethyl isocyanide (TosMIC) in ionic liquid 1‐butyl‐3‐methylimidazolium bromide ([bmIm]Br) was developed. The reactions were performed at room temperature with KOH as base with good yields in a short time (about 2 h). Some tough conditions, such as absolutely anhydrous organic solvents, low temperature, hazardous and expensive strong base or organic base, were not needed. The yields of 4(3)‐substituted 3(4)‐nitro‐1H‐pyrroles were moderate, but excellent yields were achieved for the preparation of 3‐substituted 4‐methyl‐2‐tosyl‐1H‐pyrroles. This strategy was quite general and it worked in a broad range of nitroolefins with aromatic, aliphatic or heterocyclic substituents. The recovered ionic liquid could be reused as solvent for several times without significant decrease of reaction yields.