“…The ylide carbon atom of 3a could abstract the amide proton and a following elimination of triphenylphosphine oxide would generate II ( vide infra ). Then, the ketenimine could be transformed to aminonaphthalene 4a via 6π‐electrocyclic ring closure (ERC) process …”
Section: Methodsmentioning
confidence: 99%
“…The amide ylide 3a could form unstable oxaphosphetane intermediate, 12a and a following elimination of Ph 3 PO would generate ketenimine intermediate II . Thermal 6π‐electrocyclization of II and a subsequent 1,3‐proton transfer could furnish 4a …”
Morita-Baylis-Hillman (MBH) adducts have been used extensively for the synthesis of various cyclic and acyclic compounds. 1 One of the important chemical transformations of MBH adducts starts from a conversion of electrophilic β-carbon of acrylate moiety to a nucleophilic center by forming MBH adduct-derived phosphorous ylide I, as shown in Scheme 1. 2,3 The MBH ylide I could be formed by the reaction of MBH bromide or acetate with tertiary phosphine in the presence of base, 2 and the ylide has been used for the synthesis of Ramirez ylides, 2a spirooxindoles, 2b,c poly-substituted aromatics, 2e-h and 1,3dienes. 2i-k The ylide I could also be generated more efficiently from MBH carbonate 1a and tertiary phosphine without an external base, 3 and the ylide has been used extensively for the synthesis of thiophenes, 3a pyrazoles, 3b isoquinolines, 3c butenolides, 3e and spirooxindoles. 3o Very recently, we reported a stereoselective synthetic method of 3,4-dibenzylidenepyrrolidine-2,5-diones by the reaction of ylide I and phenyl isocyanate (2a) to form carbamoyl stabilized ylide 3a, and a following Wittig reaction with benzaldehyde (Scheme 1). 4 The amide proton of 3a was eliminated during the acid-catalyzed cyclization as MeOH. As a continuous work, we envisioned that ylide 3a could be converted to ketenimine intermediate II by liberation of triphenylphosphine oxide in the absence of an acid catalyst at elevated temperature. The ylide carbon atom of 3a could abstract the amide proton and a following elimination of triphenylphosphine oxide would generate II (vide infra). Then, the ketenimine could be transformed to aminonaphthalene 4a 5 via 6π-electrocyclic ring closure (ERC) process. [6][7][8] In order to check the feasibility of our assumption, a toluene solution of 3a 4 was heated to reflux for 3 h. To our delight, methyl 4-phenylaminonaphthalene-2-carboxylate (4a) was obtained in good yield (72%). When we used benzene as a solvent, a long reaction time (20 h) was required and the yield was moderate (51%). In addition, 4a could be synthesized directly from MBH carbonate 1a in one-pot procedure in good yield (63%) by the reaction of 1a and PPh 3 (1.1 equiv) in toluene at room temperature (5 min) to form I, addition of phenyl isocyanate (2a, 1.1 equiv) to form 3a (80 C, 1 h), and a final heating to reflux of the reaction mixture (3 h). 9 The yield of one-pot reaction (63%) was better than the two-pot procedure (68/72% = 49%). The structure of 4a was confirmed unequivocally by its crystal structure, and the structure of 4a is shown in Scheme 1 along with the crystal structure of 3a. 4,10 Encouraged by the successful result various MBH carbonates 1b-1h were prepared, 3,4 and the reactions with some representative isocyanates 2a-2d have been carried out in one-pot manner. The results are summarized in Table 1. The reactions of 1b and 1c afforded 4b (52%) and 4c (54%) in moderate yields. The reaction of 4-nitrophenyl derivative 1d afforded 4d in somewhat lower yield (44%). The reactions of 1e-1g afforded 4e-4g in moder...
“…The ylide carbon atom of 3a could abstract the amide proton and a following elimination of triphenylphosphine oxide would generate II ( vide infra ). Then, the ketenimine could be transformed to aminonaphthalene 4a via 6π‐electrocyclic ring closure (ERC) process …”
Section: Methodsmentioning
confidence: 99%
“…The amide ylide 3a could form unstable oxaphosphetane intermediate, 12a and a following elimination of Ph 3 PO would generate ketenimine intermediate II . Thermal 6π‐electrocyclization of II and a subsequent 1,3‐proton transfer could furnish 4a …”
Morita-Baylis-Hillman (MBH) adducts have been used extensively for the synthesis of various cyclic and acyclic compounds. 1 One of the important chemical transformations of MBH adducts starts from a conversion of electrophilic β-carbon of acrylate moiety to a nucleophilic center by forming MBH adduct-derived phosphorous ylide I, as shown in Scheme 1. 2,3 The MBH ylide I could be formed by the reaction of MBH bromide or acetate with tertiary phosphine in the presence of base, 2 and the ylide has been used for the synthesis of Ramirez ylides, 2a spirooxindoles, 2b,c poly-substituted aromatics, 2e-h and 1,3dienes. 2i-k The ylide I could also be generated more efficiently from MBH carbonate 1a and tertiary phosphine without an external base, 3 and the ylide has been used extensively for the synthesis of thiophenes, 3a pyrazoles, 3b isoquinolines, 3c butenolides, 3e and spirooxindoles. 3o Very recently, we reported a stereoselective synthetic method of 3,4-dibenzylidenepyrrolidine-2,5-diones by the reaction of ylide I and phenyl isocyanate (2a) to form carbamoyl stabilized ylide 3a, and a following Wittig reaction with benzaldehyde (Scheme 1). 4 The amide proton of 3a was eliminated during the acid-catalyzed cyclization as MeOH. As a continuous work, we envisioned that ylide 3a could be converted to ketenimine intermediate II by liberation of triphenylphosphine oxide in the absence of an acid catalyst at elevated temperature. The ylide carbon atom of 3a could abstract the amide proton and a following elimination of triphenylphosphine oxide would generate II (vide infra). Then, the ketenimine could be transformed to aminonaphthalene 4a 5 via 6π-electrocyclic ring closure (ERC) process. [6][7][8] In order to check the feasibility of our assumption, a toluene solution of 3a 4 was heated to reflux for 3 h. To our delight, methyl 4-phenylaminonaphthalene-2-carboxylate (4a) was obtained in good yield (72%). When we used benzene as a solvent, a long reaction time (20 h) was required and the yield was moderate (51%). In addition, 4a could be synthesized directly from MBH carbonate 1a in one-pot procedure in good yield (63%) by the reaction of 1a and PPh 3 (1.1 equiv) in toluene at room temperature (5 min) to form I, addition of phenyl isocyanate (2a, 1.1 equiv) to form 3a (80 C, 1 h), and a final heating to reflux of the reaction mixture (3 h). 9 The yield of one-pot reaction (63%) was better than the two-pot procedure (68/72% = 49%). The structure of 4a was confirmed unequivocally by its crystal structure, and the structure of 4a is shown in Scheme 1 along with the crystal structure of 3a. 4,10 Encouraged by the successful result various MBH carbonates 1b-1h were prepared, 3,4 and the reactions with some representative isocyanates 2a-2d have been carried out in one-pot manner. The results are summarized in Table 1. The reactions of 1b and 1c afforded 4b (52%) and 4c (54%) in moderate yields. The reaction of 4-nitrophenyl derivative 1d afforded 4d in somewhat lower yield (44%). The reactions of 1e-1g afforded 4e-4g in moder...
“…To this end, another group within our laboratories had developed an efficient method for the preparation of 1a based on the same disconnection by the cyclisation of the acrylamide 5 using Ph 3 P/C 2 Cl 6 /Et 3 N at 110−120 °C . It was nevertheless considered expedient to discover and screen as many strategically new routes to 1a (and therefore 1b ) as possible, with a view to finding the most efficient and cost effective processes to these compounds.…”
Section: Resultsmentioning
confidence: 99%
“…The 3,4,8-trisubstituted quinoline derivatives 3-butyryl-8-methoxy-4-[(2-methylphenyl)amino]quinoline ( 1a ) and 3-butyryl-8-(2-hydroxyethoxy)-4-[(2-methylphenyl)amino]quinoline ( 1b ) emerged from SmithKline Beecham's gastrointestinal research programme as reversible (H + /K + ) ATPase inhibitors for the treatment of peptic ulcers, gastro-oesophageal reflux disease, and related disorders and have been described previously. − This paper summarises exploratory work on a number of alternative routes to these compounds and describes how one route was developed into a viable commercial synthesis. Each of the five general strategies explored featured one of the disconnections a−e shown in Figure as a basis for the critical conversions.…”
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“…[22] In contrast with the 6π-electrocyclizations shown above, in the conversion 55 Ǟ 56 the cumulated C=C double bond of the ketenimine, and not its N=C double bond, is the one forming part of the hexatrienic system involved in the electrocyclization. [22] In contrast with the 6π-electrocyclizations shown above, in the conversion 55 Ǟ 56 the cumulated C=C double bond of the ketenimine, and not its N=C double bond, is the one forming part of the hexatrienic system involved in the electrocyclization.…”
Selected recent developments in the chemistry of ketenimines are presented, demonstrating that heterocumulenes of this class are versatile reactive intermediates in the synthesis of nitrogenated heterocycles. This microreview includes examples of intramolecular nucleophilic and radical additions, biradical cyclizations, 4π‐ and 6π‐electrocyclic ring closures, [2+2], [3+2] and [4+2] cycloadditions, ketenimine‐to‐nitrile rearrangements and 1,3‐X, 1,5‐X and 1,5‐H shifts.
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