Synthesis of tetrahydroquinazolines from 2-aminobenzonitriles and alkylidene malonates via 1,4-conjugate addition and an unprecedented rearrangement reaction

An efficient methodology for the synthesis of highly diverse tetrahydroquinazoline scaffolds from 2-aminobenzonitriles and alkylidene malonates via 1,4-conjugate addition followed by an unprecedented rearrangement has been demonstrated. The methodology is further applicable for the synthesis of quinazolines and tetracyclic compounds. Some of the synthesized compounds exhibit photophysical properties.

Transition metal-free regioselective direct acylation of quinazolines for the synthesis of acylquinazoline derivatives

An efficient, mild method for direct regioselective acylation of quinazolines under metal-free conditions was developed with bis(trifluoroacetoxy)iodobenzene and trimethylsilyl azide at ambient temperature. The acylation reaction of quinazolines with aldehydes gave the corresponding acyl quinazolines in ethyl acetate with good to excellent yields and excellent functional group tolerance and site selectivity. In addition, the mechanism of the direct acylation of quinazolinone was investigated through HPLC-HRMS (high pressure liquid chromatography-high resolution mass spectrometry) and EPR (electron paramagnetic resonance) strategies.

Late-stage diversification of indole skeletons through nitrogen atom insertion

Compared with peripheral late-stage transformations mainly focusing on carbon-hydrogen functionalizations, reliable strategies to directly edit the core skeleton of pharmaceutical lead compounds still remain scarce despite the recent flurry of activity in this area. Herein, we report the skeletal editing of indoles through nitrogen atom insertion, accessing the corresponding quinazoline or quinoxaline bioisosteres by trapping of an electrophilic nitrene species generated from ammonium carbamate and hypervalent iodine. This reactivity relies on the strategic use of a silyl group as a labile protecting group that can facilitate subsequent product release. The utility of this highly functional group-compatible methodology in the context of late-stage skeletal editing of several commercial drugs is demonstrated.

Catalytic Aerobic Oxidation of C(sp3 )-H Bonds

Oxidation reactions are a key technology to transform hydrocarbons from petroleum feedstock into chemicals of a higher oxidation state, allowing further chemical transformations. These bulk-scale oxidation processes usually employ molecular oxygen as the terminal oxidant as at this scale it is typically the only economically viable oxidant. The produced commodity chemicals possess limited functionality and usually show a high degree of symmetry thereby avoiding selectivity issues. In sharp contrast, in the production of fine chemicals preference is still given to classical oxidants. Considering the strive for greener production processes, the use of O₂ , the most abundant and greenest oxidant, is a logical choice. Given the rich functionality and complexity of fine chemicals, achieving regio/chemoselectivity is a major challenge. This review presents an overview of the most important catalytic systems recently described for aerobic oxidation, and the current insight in their reaction mechanism.

Synthesis of 4-benzylpyridines via Pd-catalyzed CH3-arylation of 4-picoline

A highly efficient synthesis of 4-benzylpyridines was developed via Pd-catalyzed C(sp³)–H arylation between 4-picoline and aryl halides. It was found that the best yields were achieved with a simple Pd(PPh₃)₄ catalyst and Cs₂CO₃ as the base.

Tandem C(sp3)-H Arylation/Oxidation and Arylation/Allylic Substitution of Isoindolinones

Isoindolinones comprise an important class of medicinally active compounds. Herein we report a straightforward functionalization of the isoindolinones with aryl bromides (22 examples) using a Pd(OAc)2/NIXANTPHOS-based catalyst system. Additionally 3-aryl 3-hydroxy isoindolinone derivatives, which exhibit anti-tumor activity, can be accessed via a tandem reaction. Thus, when the arylation product is exposed to air under basic conditions, in situ oxidation takes place to install the 3-hydroxyl group. Furthermore, a tandem arylation/allylic substitution reaction is advanced in which both the arylation and allylic substitution are catalyzed by the same palladium catalyst. Finally, a tandem arylation/alkylation procedure is presented. These tandem reactions enable the synthesis of a variety of structurally diverse isoindolinone derivatives from common starting materials.

Palladium-Catalyzed Benzylic Arylation of Pyridylmethyl Silyl Ethers: One-Pot Synthesis of Aryl(pyridyl)methanols

An efficient palladium-catalyzed direct arylation of pyridylmethyl silyl ethers with aryl bromides is described. A Pd(OAc)2/NIXANTPHOS-based catalyst provides aryl(pyridyl)methyl alcohol derivatives in good to excellent yields (33 examples, 57-100% yield). This protocol is compatible with different silyl ether protecting groups, affording either the protected or the free alcohols in an effective one-pot process. The scalability of the reaction is demonstrated.

Chemoselective Palladium-Catalyzed Deprotonative Arylation/[1,2]-Wittig Rearrangement of Pyridylmethyl Ethers

Control of chemoselectivity is one of the most challenging problems facing chemists and is particularly important in the synthesis of bioactive compounds and medications. Herein, the first highly chemoselective tandem C(sp3)-H arylation/[1,2]-Wittig rearrangement of pyridylmethyl ethers is presented. The efficient and operationally simple protocols enable generation of either arylation products or tandem arylation/[1,2]-Wittig rearrangement products with remarkable selectivity and good to excellent yields (60-99%). Choice of base, solvent, and reaction temperature play a pivotal role in tuning the reactivity of intermediates and controlling the relative rates of competing processes. The novel arylation step is catalyzed by a Pd(OAc)2/NIXANTPHOS-based system via a deprotonative cross-coupling process. The method provides rapid access to skeletally diverse aryl(pyridyl)methanol core structures, which are central components of several medications.

Base catalysed intermolecular cyclisation of N-protected o-amino benzaldehyde/acetophenone with phosphorus/sulphur based allenes: facile synthesis of substituted quinolines

Base catalyzed reaction of N-Bz protected o-aminobenzaldehyde with allenylphosphonates affords O-phosphorylated quinolines via a route involving a thermal rearrangement.

Palladium-Catalyzed Benzylic C-H Arylation of Azaarylmethylamines

A direct C-H functionalization approach to produce aryl(azaaryl)methylamines from azaarylmethylamines without directing groups is described. Under conditions where the azaarylmethylamines' C-H is reversibly deprotonated, a Pd(OAc)(2)/NIXANTPHOS-based catalyst couples the resulting carbanions with various aryl halides to provide aryl(azaaryl)methylamines. This umpolung strategy directly provides tertiary amines without protecting or activating groups.

Traceless Solid-Phase Synthesis of Trisubstituted Quinazolines

A traceless polymer-supported synthesis of 4-benzoylquinazolines was developed using the following commercially available building blocks: Fmoc-α-amino acids, 2-nitrobenzensulfonyl chlorides and α-bromoacetophenones. The acyclic intermediates underwent base-catalyzed rearrangement involving C-C and N-N bond formation followed by ring expansion and yielded resin-bound dihydroquinazoline-2-carboxylic acids. After they were released from the resin by treatment with trifluoroacetic acid, base-mediated decarboxylation produced the target quinazolines in moderate-to-high yields and purities.

Synthesis of triarylmethanols via tandem arylation/oxidation of diarylmethanes

A tandem arylation/oxidation of diarylmethanes for the convenient synthesis of unsymmetrical triarylmethanols bearing different aryl and heteroaryl groups is described. A Pd(OAc)2-NiXantphos catalyst system efficiently catalyzed arylation of weakly acidic sp3-hybridized C-H bonds of diarylmethanes with aryl bromides, and the arylation products were then oxidized in situ to carbinols by simply opening the reaction flasks to air. The triarylmethanol products were obtained in 35-98% yield.

Palladium(II)-catalyzed intramolecular tandem aminoalkylation via divergent C(sp3)-H functionalization

We have developed a Pd(II)-catalyzed oxidative tandem aminoalkylation via divergent C(sp(3))-H functionalization, affording three- and five-membered-ring fused indolines in good yields under two optimized conditions, respectively. The mechanism studies have indicated that the benzylic C-H cleavage involved in the former transformation is the rate-determining step, while the cleavage of amide α-C-H in the latter is not. This is the first example of a Pd-catalyzed tandem reaction involving C(sp(3))-H activation without the employment of prefunctionalized reagents (e.g., halogenated and boron reagents) and directing groups, representing a green and economic protocol for the construction of N-containing heterocycles.

Utilization of methylarenes as versatile building blocks in organic synthesis

This review attempts to describe the latest developments in the utilisation of methylarenes adopting C–H functionalization strategies and covers all the developments until March 2015.

Palladium-catalyzed one pot 2-arylquinazoline formation via hydrogen-transfer strategy

The palladium catalytic system was first applied to 2-arylquinazoline synthesis via hydrogen transfer methodology. Various (E)-2-nitrobenzaldehyde O-methyl oximes reacted easily with alcohols or benzyl amines to provide N-heterocyclic compounds in good to high yields. Similarly, the heterocyclic products could be prepared by the reaction of 1-(2-nitrophenyl)ethanone, urea and benzyl alcohols. In these reactions, the nitro group was reduced in situ by hydrogen generated from the alcohol dehydrogenation step.

Metal-free oxidative synthesis of quinazolinones via dual amination of sp3 C–H bonds

A novel metal-free synthesis of quinazolinones via dual amination of sp³ C–H bonds was developed. The sp³ carbon in methylarenes or adjacent to a heteroatom in DMSO, DMF or DMA was used as the one carbon synthon.

n-Bu4NI-catalyzed selective dual amination of sp3 C–H bonds: oxidative domino synthesis of imidazo[1,5-c]quinazolines on a gram-scale

A facile and efficient approach to the synthesis of imidazo[1,5-c]quinazolines was developed via a tandem reaction following dual sp³ C–H amination under metal-free conditions.