Application of Nazarov type electrocyclization to access [6,5,6] and [6,5,5] core embedded new polycycles: an easy entry to tetrahydrofluorene scaffolds related to Taiwaniaquinoids and C-nor-D homosteroids

Metal-free thiolation of sulfonyl hydrazone with thiophenol: synthesis of 4-thio-chroman and diarylmethyl thioethers

A simple, efficient, and transition metal-free approach was developed for accessing 4-thio-substituted chroman and diarylmethyl thioethers from sulfonyl hydrazones. This protocol provides straightforward access to a class of diarylmethane derivatives with good to excellent yields. This operationally simple protocol exhibited good tolerance for labile functional groups, providing biologically relevant chemical libraries. This safe and feasible route is applicable to the large-scale synthesis of 4-thio-substituted chromans, which are of great synthetic interest because of their further reaction potential.

Novel d-Annulated Pentacyclic Steroids: Regioselective Synthesis and Biological Evaluation in Breast Cancer Cells

The acid-catalyzed cyclization of benzylidenes based on 16-dehydropregnenolone acetate (16-DPA) was studied. It was found that these compounds readily undergo regioselective interrupted Nazarov cyclization with trapping chloride ion and an efficient method of the synthesis of d-annulated pentacyclic steroids based on this reaction was proposed. The structures of the synthesized pentacyclic steroids were determined by NMR and X-ray diffraction. It was found that the reaction affords a single diastereomer, but the latter can crystallize as two conformers depending on the structure. Antiproliferative activity of synthesized compounds was evaluated against two breast cancer cell lines: MCF-7 and MDA-MB-231. All tested compounds showed relatively high antiproliferative activity. The synthetic potential of the protocol developed was illustrated by the gram-scale experiment.

Indium triflate catalysed 3-aza-Cope rearrangement of amino acid derived α,β-unsaturated esters to alkylidene oxindoles

The first examples of amino acid derived α,β-unsaturated esters to Z-alkylidene oxindoles via 3-aza-Cope rearrangement using In(OTf)₃ are reported.

Nazarov reaction: current trends and recent advances in the synthesis of natural compounds and their analogs

Recent applications of the Nazarov reaction to stereoselective synthesis of pharmacology-relevant cyclopentenone scaffolds are summarized.

Nazarov cyclization of 1,4-pentadien-3-ols: preparation of cyclopenta[b]indoles and spiro[indene-1,4'-quinoline]s

The first Lewis acid-catalyzed intramolecular interrupted Nazarov cyclization of 1,4-pentadien-3-ols is described. Using FeBr3 as the catalyst, a series of new substituted cyclopenta[b]indoles was prepared-through a sequence of Nazarov cyclization, nucleophilic amination, and isomerization-with good yields and high diastereo- and regioselectivities. A similar catalytic process was also developed for the synthesis of structurally interesting spiro[indene-1,4'-quinoline]s.

Microwave assisted [RuCl2(p-cymene)2]2 catalyzed regioselective endo-tandem cyclization involving imine and alkyne activation: an approach to benzo[4,5]imidazo[2,1-a]pyridine scaffold

A microwave assisted efficient route to the synthesis of benzimidazole fused heterocycles through metal catalyzed endo-cyclization strategy involving imine and alkyne activation has been developed.

Efficient synthesis of bicyclo[6.3.0]undecadienones by Nazarov cyclization/regioselective elimination

Easily accessible cyclooctadienyl vinyl ketones can generate fused bicyclic 8-5 (bicyclo[6.3.0]undecadienone) ring systems via the Nazarov cyclization when treated with Lewis acid. The resultant products contain three new stereocenters as well as olefins suitably situated to allow further structural elaboration. This concise sequence allows for the rapid preparation of intermediates that should be applicable to a variety of natural product targets containing this bicyclic core.

Beyond the Divinyl Ketone: Innovations in the Generation and Nazarov Cyclization of Pentadienyl Cation Intermediates

The requirement for new strategies for synthesizing five-membered carbocycles has driven an expansion in the study of the Nazarov cyclization. This renewed interest in the reaction has led to the discovery of several interesting new methods for generating the pentadienyl cation intermediate central to the cyclization. Methods reviewed include carbon-heteroatom ionization, functionalization of a double bond, nucleophilic addition, or electrocyclic ring opening. Additional variations employ unconventional substrates to produce novel pentacycles, such as the iso- and imino-Nazarov. Herein, we provide an overview of these unconventional, yet highly useful versions of the Nazarov cyclization.