28586-48-3Relevant academic research and scientific papers
Chiral Phosphoric Acid Catalyzed Kinetic Resolution of 2-Amido Benzyl Alcohols: Asymmetric Synthesis of 4H-3,1-Benzoxazines
Rajkumar, Subramani,Tang, Mengyao,Yang, Xiaoyu
supporting information, p. 2333 - 2337 (2020/01/08)
An efficient method for the asymmetric synthesis of 4H-3,1-benzoxazines was developed by kinetic resolution of 2-amido benzyl alcohols using chiral phosphoric acid catalyzed intramolecular cyclizations. A broad range of benzyl alcohols (both secondary and tertiary alcohols) were kinetically resolved with high selectivities, with an s factor of up to 94. Mechanistic studies were performed to elucidate the mechanism of these reactions, wherein the amide moieties reacted as the electrophiles. Gram-scale reaction and facile transformations of the chiral products demonstrate the potential of this method in asymmetric synthesis of biologically active chiral heterocycles.
"Site Selective" Formation of Low-Valent Titanium Reagents: An "Instant" Procedure for the Reductive Coupling of Oxo Amides to Indoles
Fuerstner, Alois,Hupperts, Achim,Ptock, Arne,Janssen, Edo
, p. 5215 - 5229 (2007/10/02)
Aromatic acylamido carbonyl compounds are readily cyclized to indole derivatives upon treatment with low-valent titanium reagents of the formal oxidation states 0, +1, and +2.Other strong reducing agents such as SmI2 and low-valent zirconium, niobium, and tungsten complexes are also capable of effecting such intramolecular alkylidenation reactions of amides.From the preparative point of view these heterocycle syntheses are best effected with an active titanium species which is prepared in the presence of the carbonyl compound upon coordination of TiCln (n = 3, 4) to the oxo amide substrate and reduction of this complex with zinc dust ("instant" method).This procedure turned out to be as effective as the titanium-graphite-based methodology previously described but is much easier to perform as all hazardous reagents are avoided. "Instant" cyclizations can also be run in nonetheral solvents such as DMF, ethyl acetate, or acetonitrile and turned out to be compatible with many functional groups.The method was used to cyclize oxo amide 15 to (+)-aristoteline, and it applies nicely to the synthesis of strained indole derivatives, the formation of benzofurans, conventional McMurry reactions of aldehydes and ketones, and the dimerization of alkynes.Metals such as zirconium can also be activated in situ by reduction of ZrCl4 in the presence of a carbonyl compound.On the basis of the results obtained with substrates bearing appropriate structural probes a mechanism for such intramolecular keto-amide coupling processes is proposed.Carbonyl dianions, formed upon two-electron reduction of the keto group, are the most likely reactive intermediates.Electrochemical investigations support this mechanistic interpretation.
Heterocyclic 8?-Systems, 15. Investigations on Indole 2,3-Oxides: Sythesis of 3-Hydroxyindoles via Intramolecular Wittig-Rearrangement of 1,2-Dihydro-4H-3,1-benzoxazines
Schmidt, Richard R.,Beitzke, Bernhard
, p. 2115 - 2135 (2007/10/02)
Investigations to trap indole 2,3-oxides 11 by base catalyzed ring contraction of 4H-3,1-benzoxazines 3 led in the system KNH2/NH3 to 3-hydroxy-3H-indoles 7.The N-methylbenzoxazinium salts 15, obtained from 3 and FSO3CH3, yielded with ethoxide under kinet
