Tandem Pseudopericyclic Reactions: [1,5]-X Sigmatropic Shift/6-Electrocyclic Ring Closure Converting N-(2-X-Carbonyl)phenyl Kete

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Tandem Pseudopericyclic Reactions: [1,5]-X Sigmatropic Shift/6-Electrocyclic Ring Closure Converting N-(2-X-Carbonyl)phenyl Kete

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作者：Mateo Alajarí ; n ; Marí ; a-Mar Ortí ; n ; Pilar S&aacute ; nchez-Andrada ; &Aacute ; ngel Vidal
刊名：Journal of Organic Chemistry
出版年：2006
出版时间：October 13, 2006
年：2006
卷：71
期：21
页码：8126 - 8139
全文大小：675K
年卷期：v.71,no.21(October 13, 2006)
ISSN：1520-6904

文摘

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N-(2-X-Carbonyl)phenyl ketenimines undergo, under mild thermal conditions, [1,5]-migration of the Xgroup from the carbonyl carbon to the electron-deficient central carbon atom of the ketenimine fragment,followed by a 6

s/gifchars/pi.gif" BORDER=0 >-electrocyclic ring closure of the resulting ketene to provide 2-X-substituted quinolin-4(3H)-ones in a sequential one-pot manner. The X groups tested are electron-donor groups, such asalkylthio, arylthio, arylseleno, aryloxy, and amino. When involving alkylthio, arylthio, and arylselenogroups, the complete transformation takes place in refluxing toluene, whereas for aryloxy and aminogroups the starting ketenimines must be heated at 230

s/entities/deg.gif">C in a sealed tube in the absence of solvent. Themechanism for the conversion of these ketenimines into quinolin-4(3H)-ones has been studied by abinitio and DFT calculations, using as model compounds N-(2-X-carbonyl)vinyl ketenimines bearingdifferent X groups (X = F, Cl, OH, SH, NH₂, and PH₂) converting into 4(3H)-pyridones. Thiscomputational study afforded two general reaction pathways for the first step of the sequence, the [1,5]-X shift, depending on the nature of X. When X is F, Cl, OH, or SH, the migration occurs in a concertedmode, whereas when X is NH₂ or PH₂, it involves a two-step sequence. The order of migratory aptitudesof the X substituents at the acyl group is predicted to be PH₂ > Cl > SH > NH₂ > F> OH. The secondstep of the full transformation, the 6

s/gifchars/pi.gif" BORDER=0 >-electrocyclic ring closure, is calculated to be concerted and withlow energy barriers in all the cases. We have included in the calculations an alternative mode of cyclizationof the N-(2-X-carbonyl)vinyl ketenimines, the 6

s/gifchars/pi.gif" BORDER=0 >-electrocyclic ring closure leading to 1,3-oxazines thatinvolves its 1-oxo-5-aza-1,3,5-hexatrienic system. Additionally, the pseudopericyclic topology of thetransition states for some of the [1,5]-X migrations (X = F, Cl, OH, SH), for the 6

s/gifchars/pi.gif" BORDER=0 >-electrocyclizationof the ketene intermediates to the 4(3H)-pyridones, and for the 6

s/gifchars/pi.gif" BORDER=0 >-electrocyclization of the startingketenimines into 1,3-oxazines could be established on the basis of their geometries, natural bond orbitalanalyses, and magnetic properties. The calculations predict that the 4(3H)-pyridones are the thermodynamically controlled products and that the 1,3-oxazines should be the kinetically controlled ones.