Thiazolo[3,4- b ]indazole-2,2-dioxides as Masked Extended Dipoles: Pericyclic Reactions of Benzodiazafulvenium Methides (original) (raw)
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A Versatile Synthesis of Substituted Indazoles
HETEROCYCLES, 1995
A four-step synthetic sequence for substituted indazoles was presented from 2-acylcyclohexane-1.3-diones via either simultaneous or stepwise dehydration and dehydrogenation of 4-substituted 4-hydroxy-4.5.6.7tetrahydroindazoles as a key step. The synthetic methods for indazole nucleus are somewhat limited to involve condensation of hydrazino group,' generated by in situ reduction of diazo group in c-diazophenyl ketones, with C-0 of the substi tuent at the neighboring posi tion, and dehydrogenation of 4.5,6,7-tetrahydroindazoles. The former method, however, is suffering from low yields, limitations of employable diazophenyl ketone^,^ explosive intermediates.' and the latter method is also suffering from extreme reaction conditions5 as well as low yields.' Other methods have been reported, but so far not so effective to overcome the limitations of introducing substituent on indazole skeletons, especially at C3 and/or ~4 .~ In the present paper, we describe a facile and efficient route for the preparation of indazoles, in which substituents can be easily introduced at C3 andlor Ca. RESULTS AND DISCUSSION Our strategy stems from the idea that the introduction of a proper leaving group on the tetrahydroindazole system may affect the dehydrogenation step. Upon this rationale, 4-hydroxy-4.5,6.7-tetrahydroindazoles were selected as key intermediates, which may readily undergo either stepwise or simultaneous dehydration and dehydrogenation. The synthetic sequence is, thus, quite straightforward as shown in Scheme I. The prerequisite 2-acylcyclohexane-1.3-diones (1) were prepared by previously reported methods either direct acylation7 of cyclohexane-1.3-dione or via Fries rearrangements of 3-acylow-2-cyclohexenones9 in 88.92% yields. The latter procedure gave better yields, 8 as reported. It is worthy to note that I3c nmr spectral data provided information for the enol-keto tautomerism on 2-acylcyclohexane-1.3-diones. The presence of one sp2 carbon resonance (6 112.0) and three carbonyl resonances at 6 194.9. 199.0, and 210.3 implies that keto form is the major component in compound (la) on the "C nmr scale. In the system with aromatic ring, compound (lb), however, four 2 additional sp carbon resonances appeared at 6 127.5. 128.1. 131.9. 134.2 with disappearance of the two sp3 carbon resonances at 6 32.1. and 37.9, representing G and Cs, respectively. and one carbonyl resonance was shown at 6 198.7. This impies that enol form is the major component in compound (Ib). On
Synthesis of Substituted 1H-Indazoles by Pyrazole Annelation to an Arene
Chemistry of Heterocyclic Compounds, 2013
Substituted 1H-indazoles have been synthesized by reductive intramolecular heterocyclization of 2,4-diaroyl-N-nitrosomethylanilines and 2,4-diacetyl-N-nitrosomethylaniline. The N-nitrosoanilines were obtained by nitrosation of N-methyl-2,4-diaroyl-and 2,4-diacetylanilines, the products of quaternary 3,5-diaroyl-and 3,5-diacetylpyridinium salt recyclization.
Efficient Synthesis of 7-Substituted or 3,7-Disubstituted 1 H -Indazoles
Synlett, 2007
Abstract: This work reports on the synthesis of the novel indazole scaffolds 7-OTf-1H-indazole (trifluoromethanesulfonic acid 1Hindazol-7-yl ester), 7-iodo-1H-indazole and 3-bromo-7-iodo-1Hindazole. These new compounds are potent building blocks in divergent syntheses of indazoles via palladium cross-coupling reactions.
Efficient Synthesis of 7-Substituted or 3,7-Disubstituted 1H-Indazoles
Synlett, 2007
This work reports on the synthesis of the novel indazole scaffolds 7-OTf-1H-indazole (trifluoromethanesulfonic acid 1Hindazol-7-yl ester), 7-iodo-1H-indazole and 3-bromo-7-iodo-1Hindazole. These new compounds are potent building blocks in divergent syntheses of indazoles via palladium cross-coupling reactions.
Organic Letters, 2010
A variety of nucleophiles-thiolates, alkoxides, amines, iodide, and cyanide-react with oxazino-, oxazolino-, and benzoxazin[3,2-b]indazoles under microwave conditions to yield a diverse set of 2-substituted 1 H-indazolones. The synthetic utility of these indazoles is further demonstrated by ANRORC (Addition of the Nucleophile, Ring Opening, and Ring Closure) reactions to yield isomeric pyrazoloindazolones by a process wherein iodide acts first as a nucleophile and subsequently as a leaving group. The indazole ring and its derivatives have been reported to exhibit analgesic, 1 antitumor, 2 anticancer, 3 anti-inflammatory, 4 and anti-fertility activity. 5 Of the two indazole isomers, 2Hindazoles are much less explored than 1H-indazoles. 6 As a continuation of our interest in the chemistry of 2H-indazoles and the related 1H-indazolones, 7 we set out to synthesize a series of 1H-indazolone derivatives as part of our commitment to the National Institute of General Medical Sciences (NIGMS) for the creation of pilot-scale libraries.
Synthesis of Novel Substituted Indazoles via Nucleophilic Substitution of Hydrogen
New four-substituted indazoles 4a-e were synthesized by regioselective nucleophilic substitution of hydrogen of N-alkyl-7-nitroindazoles 2a,b with arylacetonitriles 3a-c. Compounds 4a-e were reacted with arylsulfonyl chloride in pyridine to give some new indazole linked sulfonamides with good yields. The S N H at position C-4 of 7-nitroindazole with arylacetonitrile is confirmed by X-ray diffraction analysis of compounds 4e and 6a. C 2015 Wiley Periodicals, Inc. Heteroatom Chem. 26:374-381, 2015; View this article online at wileyonlinelibrary.com.
Dimerisation, rhodium complex formation and rearrangements of N-heterocyclic carbenes of indazoles
Beilstein journal of organic chemistry, 2014
Deprotonation of indazolium salts at low temperatures gives N-heterocyclic carbenes of indazoles (indazol-3-ylidenes) which can be trapped as rhodium complexes (X-ray analysis). In the absence of Rh, the indazol-3-ylidenes spontaneously dimerize under ring cleavage of one of the N,N-bonds and ring closure to an indazole-indole spiro compound which possesses an exocyclic imine group. The E/Z isomers of the imines can be separated by column chromatography when methanol is used as eluent. We present results of a single crystal X-ray analysis of one of the E-isomers, which equilibrate in solution as well as in the solid state. Heating of the indazole-indole spiro compounds results in the formation of quinazolines by a ring-cleavage/ring-closure sequence (X-ray analysis). Results of DFT calculations are presented.