A Direct and an Efficient Regioselective Synthesis of 1,2-Benzothiazine 1,1-dioxides, β-Carbolinones, Indolo[2,3-c]pyran-1-ones, Indolo[3,2-c]pyran-1-ones, Thieno[2,3-c]pyran-7-ones and Pyrano[3’,4’:4,5]imidazo[1,2-a]pyridin-1-ones via Tandem Stille/Heterocyclization Reaction
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Abstract:
A general regioselective one-pot synthesis of 1,2-benzothiazine 1,1-dioxides from 2-iodo benzenesulfonamide moieties and allenylstannanes is described using a domino Stille-like/Azacyclization reaction. The conditions developed also opened a novel access to β-carbolinones, indolopyranones, thienopyranones and pyrano-imidazopyridines.Keywords:
Pyran
Benzothiazine
Domino
Stille reaction
A general regioselective one-pot synthesis of 1,2-benzothiazine 1,1-dioxides from 2-iodo benzenesulfonamide moieties and allenylstannanes is described using a domino Stille-like/Azacyclization reaction. The conditions developed also opened a novel access to β-carbolinones, indolopyranones, thienopyranones and pyrano-imidazopyridines.
Pyran
Benzothiazine
Domino
Stille reaction
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β-Aminoenones react with monoalkyl hydrazines to give regioselectively 1,3,5-trisubstituted pyrazoles. The mechanism and level of regioselectivity depend on both the substitution pattern of the substrates and the reaction conditions. When the least bulky substituent is attached at the β-position of the enone, a high regioselectivity is obtained, usually higher than that from equivalent β-diketones. If the β-substituent is the bulkiest group, the regioselectivity decreases. Nevertheless, in the conditions reported in this paper, it is possible to prepare pyrazoles not obtainable from β-diketones.
Enone
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5-Carboalkoxy-2,3-dihydropyran-4-ones synthesised via domino C-acylation/6π-oxaelectrocyclization protocol was employed as a starting material for the first three step total synthesis of dihydronaphthopyran-4-one class of natural products.
Domino
Dihydropyran
Pyran
Cascade reaction
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Benzothiazine
Triethyl orthoformate
Condensation reaction
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Pyrazole is the ubiquitous sub-structure of many natural products and biologically active compounds. In this respect, its regioselective synthesis drew a lot of attention from synthetic organic chemists, leading to the development of various regioselective modifications of the classical Knorr cyclocondensation reaction and alternative methods. This review covers the period of 2003 to the middle of 2009 on the regioselective synthesis of pyrazoles, which are categorized into four reaction types: (i) modified Knorr condensation reaction using 1,3-dicarbonyl surrogates; (ii) 1,3-dipolar cycloadditions approach; (iii) regioselective direct substitution reaction of the pyrazole ring system; and (iv) other methods. Keywords: Pyrazole, regioselective dipolar cycloaddition, regioselective condensation, regioselective cross-coupling
Pyrazole
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1,2- and 2,1-benzothiazines, for example, 1,2-benzothiazine-1,1-dioxides. 2,benzothiazine-2,2-dioxides, 1-alkyl/aryl-1,2-/2,1-benzothiazine-S-oxides, dibenzothiazine and polyheterocycle containing benzothiazine moiety are considered to be one of the privileged heterocyclic scaffolds with huge importances both in synthetic organic chemistry and medicinal chemistry especially in the drug industry. Numerous pioneering methodologies for asymmetric and non-asymmetric scaffold constructions have been developed. Comprehensive visions of different powerful methodologies for the synthesis of these scaffolds have been presented in this review.
Benzothiazine
Moiety
Vision
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Abstract Base‐induced cyclization of the sulfonamide (III), prepared by reaction of the sulfonyl chloride (I) with methylaminoacetonitrile (II), yields the benzothiazine (IV) mentioned in the title.
Benzothiazine
Sulfonamide
Sulfonyl
Base (topology)
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Benzothiazine
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Abstract magnified image 4 H ‐1,4‐Benzothiazine‐1,1‐dioxide derivatives were synthesized through a sequence of almost quantitative reactions. The commercial starting material 2‐(methylsulfanyl)aniline was Boc‐protected, N ‐acylated and oxidized at the sulfur atom to obtain a sulfonyl derivative. An anionic transposition of the acyl group followed by asimultaneous deprotection‐cyclization gave the title products in excellent yields. All products and intermediates were fully characterized.
Benzothiazine
Derivative (finance)
Sulfonyl
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Abstract A novel facile photoconversion of 4‐hydroxy‐1,2‐bezothiazine 1,1‐dioxides ( 3a‐e ) into 4‐ oxo ‐1,3‐2 H ‐benzothiazine 1,1‐dioxides ( 4a‐e ) and 4‐hydroxy‐2‐methyl‐ N ‐(pyridin‐2‐yl)‐2 H ‐1,2‐benzothiazine‐3‐carboxamide 1,1‐dioxide (PRX) into N‐methyl saccharin ( 2 ) upon 254 nm irradiation in methanol or acetonitrile is reported. The structures of the products have been elucidated by spectroscopic methods and single crystal X‐ray structure determination for 4a and 4d .
Benzothiazine
Saccharin
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