Nitration of Pyrrolo[2,1-a]isoquinolines

We have successfully modified a series of pyrrolo[2,1-a]isoquinolines via direct nitration under mild reaction conditions. Easily accessible nitrates including CAN, Cu(NO₃)₂·H₂O, and Fe(NO₃)₃·9H₂O all can serve as effective nitrating reagents for functionalizing pyrrolo[2,1-a]isoquinolines. Various nitro-bearing pyrrolo[2,1-a]isoquinolines have been efficiently prepared in acceptable to good yields.

Organic Nitrating Reagents

Nitro compounds are vital raw chemicals that are widely used in academic laboratories and industries for the preparation of various drugs, agrochemicals, and materials. Thus, nitrating reactions are of great importance for chemists and are even taught in schools as one of the fundamental transformations in organic synthesis. Since the discovery of the first nitrating reactions in the 19th century, progress in this field has been constant. Yet, for many years the classical electrophilic nitration approach using a mixture of strong mineral acids dominated the field. However, in recent decades, the attention of researchers has focused on new reactivity and new reagents that can provide access to nitro compounds in a practical and straightforward way under mild reaction conditions. Organic nitrating reagents have played a special role in this field since they have enhanced reactivity. They also allow nitration to be carried out in an ecofriendly and sustainable manner. This review examines the development and application of organic nitrating reagents.

1 Introduction

2 Organic Nitrating Reagents

2.1 Alkyl Nitrites

2.2 Nitroalkanes

2.3 Alkyl Nitrates

2.4 N-Nitroamides

2.5 N-Nitropyrazole

2.6 N-Nitropyridinium Salts

3 Organic Nitrating Reagents Generated In Situ

3.1 Acyl Nitrates

3.2 Trimethylsilyl Nitrate

3.3 Nitro Onium Salts

4 Organic Nitronium Salts

5 Organic Nitrates and Nitrites

5.1 Ammonium Nitrates

5.2 Heteroarylium Nitrates

5.3 Other Organic Nitrates

5.4 Organic Nitrites

6 Conclusion and Outlook

Pd-Catalyzed sp3 C-H alkoxycarbonylation of 8-methylquinolines using Mo(CO)6 as a CO surrogate

A Pd(ii)-catalyzed three-component sp³ C-H alkoxycarbonylation of 8-methylquinonlines (8-MQs) with alcohols is accomplished using the colorless crystalline Mo(CO)₆ as a CO source. The protocol is compatible with a wide range of 8-MQs and alcohols, furnishing the carbonylated adducts in moderate to good yields. The substrate scope, functional group tolerance and natural product mutation are the important practical features.

A proof of concept for cooperation from the quinone groups adjacent to N sites during the metal-free oxidation of glycerol by nitrogen-rich graphene oxide

A catalytic active site already present in an organic molecule was chemically tagged on the GO surface to prove the role of quinone groups adjacent to N sites in nitrogen-rich carbon materials for the metal-free oxidation of glycerol.

Crystal structure of 3-nitroquinoline 1-oxide, C9H6N2O3

C9H6N2O3, monoclinic, P21/n (no. 14), a = 8.7156(3) Å, b = 9.4003(3) Å, c = 19.8188(7) Å, V = 1610.12(10) Å3, Z = 8, R gt(F) = 0.0491, wR ref(F 2) = 0.1347, T = 291(2) K.

tert-Butyl nitrite-mediated radical cyclization of tetrazole amines and alkynes toward tetrazolo[1,5-a]quinolines

A general and efficient radical cyclization of 1H-tetrazol-5-amines and alkynes toward tetrazolo[1,5-a]quinolines is established for the first time. The annulation mediated by tert-butyl nitrite takes place expeditiously within 10 minutes under mild conditions. Without using external additives or excitation, the tetrazolo[1,5-a]quinoline derivatives are obtained in moderate to good yields, along with high regioselectivities for unsymmetrical alkynes and broad functional tolerance features. The reaction is exemplified to occur via a radical process, with aryl radicals synergistically generated from tert-butyl nitrite, water and tetrazolate-diazonium salts.

Copper-mediated domino C–H iodination and nitration of indoles

An efficient and cost-effective copper-mediated aerobic oxidative C–H iodination and nitration of indoles via double C–H functionalization is reported. The domino process proceeds smoothly under mild aerobic conditions to give 3-iodo-2-nitroindoles in one step with high regioselectivity and a broad substrate scope.

Metal-free deoxygenative sulfonylation of quinoline N-oxides with sodium sulfinates via a dual radical coupling process

The first example of a metal- and reductant-free deoxygenative sulfonylation of quinoline N-oxides with sodium sulfinates via a dual radical coupling process is reported.

Aryl Nitriles from Alkynes Using tert-Butyl Nitrite: Metal-Free Approach to C≡C Bond Cleavage

Alkyne C≡C bond breaking, outside of alkyne metathesis, remains an underdeveloped area in reaction discovery. Recently, nitrogenation has been reported to allow nitrile formation from alkynes. A new protocol for the metal-free C≡C bond cleavage of terminal alkynes to produce nitriles is reported. This method provides an opportunity to synthesize a vast range of nitriles containing aryl, heteroaryl, and natural product derivatives (38 examples). In addition, the potential of (t)BuONO to act as a powerful nitrogenating agent for terminal aryl alkynes is demonstrated.

The development of carbene-stabilized N–O radical coupling strategy in metal-free regioselective C–H azidation of quinoline N-oxides

The key regioselective issue of quinoline N-oxide azidation was resolved via the oxidative cross-coupling of carbene-stabilized N–O radicals and TMSN₃. Compared with the reported azidations, the present metal-free procedure is convenient and regioselective under mild conditions, and could be scaled up to gram-synthesis.

Regioselective synthesis of nitrosoimidazoheterocycles using tert-butyl nitrite

A simple and practical method has been developed for the regioselective nitrosylation of imidazopyridines via C(sp²)–H bond functionalization using tert-butyl nitrite under mild reaction conditions.

Synthesis of quinazolinimines and quinazolinamines from 2-fluorobenzonitriles under catalyst-free conditions

A convenient procedure for the synthesis of quinazolinimines and quinazolinamines from 2-fluorobenzonitriles and 2-aminopyridines or amidines with KO^tBu as the promotor has been developed.