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• W2138193399 abstract "A three-step sequence starting from N-Boc p-anisidines allowed a short synthesis of 4-aminotropones (see scheme; Boc=tert-butoxycarbonyl). Regioselective introduction of substituents at the tropone ring was controlled by choosing adequate substitution at the aniline derivative and/or the sulfoxide or sulfone used in the second step. When this is dimethyl sulfone an atom economy process occurred in which SO2 or the methtyl sulfinate anion are the byproducts. An efficient synthesis of 4-aminotropones has been achieved in excellent yields by simple treatment of 4-amino-4-[(p-tolylsulfinyl)methyl]-2,5-cyclohexadienones (p-quinamines) with NaH. The method allowed regiocontrolled access to 3-methyl, 5-methyl- and 3,5-dimethyl-substituted derivatives starting from p-quinamines with adequate substituents at the cyclohexadienone moiety and/or at the carbon linked to the sulfur function. The p-quinamines in turn were easily accessible from N-Boc p-anisidines (Boc=tert-butoxycarbonyl) by electrochemical oxidation in MeOH to quinone imine monoketals, followed by addition of a α-lithium sulfinyl carbanion to the imino group, and ketal hydrolysis. Oxidation of the sulfoxide gave the sulfonyl-substituted p-quinamines that, upon basic treatment, behave similarly. The p-quinamine 55 and bis-p-quinamine 56, resulting in the addition of the anion derived from dimethyl sulfone to the p-quinonimine ketal 14, also gave the 4-aminotropone. The mechanism involves the initial formation of a α-sulfonyl carbanion, which intramolecularly attacks the cyclohexadienone giving a norcaradiene-like enolate intermediate, the evolution of which through a ring-expansion process, pushes off a methyl sulfinate anion or SO2. This efficient process fulfils the criteria of atom economy. The introduction of a proline substituent in the nitrogen of the starting p-quinamine allowed the synthesis of an enantiopure 4-aminotropone, the asymmetric Diels–Alder reactions of which with maleimide occurred in a highly endo and π-facial diastereoselective manner. La síntesis de 4-aminotroponas se ha logrado en una única etapa y con excelentes rendimientos por tratamiento de 4-amino-4-[(p-tolilsulfinil)metil]-2,5-ciclohexadienonas (p-quinaminas) con NaH. Esta metodología permite acceder de forma regiocontrolada a 4-aminotroponas con sustituyentes metilo en distintas posiciones (3-, 5- y 3,5-) a partir de p-quinaminas adecuadamente sustituidas en el fragmento de ciclohexadienona y/o en el C-α respecto de la función de azufre. Las p-quinaminas precursoras son fácilmente accesibles a partir de p-anisidinas N-Boc protegidas por oxidación electroquímica en MeOH, para dar lugar a los monoacetales de quinonimina, seguida de adición de un α-litio sulfinil carbanión e hidrólisis del acetal. La oxidación del sulfóxido origina las sulfonil p-quinaminas que también se transforman en las 4-aminotroponas en presencia de NaH. La p-quinamina 55 y la bis-p-quinamina 56, resultantes de la adición del anión derivado de la dimetil sulfona sobre el monoacetal de quinonimina 14, también evolucionan a la 4-aminotropona en medio básico. El mecanismo del proceso implica la formación inicial de un α-sulfonil carbanión que ataca de forma intramolecular al fragmento de ciclohexadienona para dar un enolato intermedio con estructura de norcaradieno, que sufre la expansión del anillo con eliminación simultánea del anión metil sulfinato o de SO2. Este proceso cumple los requisitos de economía de átomos que aumentan su interés sintético. La introducción de un resto de prolina en el nitrógeno de la p-quinamina de partida permite acceder a una 4-aminotropona enantiopura cuyas reacciones de Diels–Alder asimétricas con maleimida tienen lugar con una elevada selectividad endo y π-facial." @default.
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• W2138193399 date "2008-01-07" @default.
• W2138193399 modified "2023-10-03" @default.
• W2138193399 title "Synthesis of 4-Aminotropones from [(Sulfinyl or Sulfonyl)methyl]-Substitutedp-Quinamines" @default.
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• W2138193399 doi "https://doi.org/10.1002/chem.200700940" @default.
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