Diels–Alder reactions of N-sulfonyl substituted aza-ortho-xylylenes generated from the corresponding 1,4-dihydro-2H-3,1-benzoxazin-2-one derivatives

Abstract

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Aza-ortho-xylylenes in Organic Synthesis

“…[88] Addition of the N-sulfonyl xylylene 157 to NPMI gives N-sulfonyl-1,2,3,4-tetrahydroquinoline (162). [87] With alkynes, such as ethynyl phenyl ketone, the initial cycloadduct 163 eliminates toluenesulfinic acid, resulting in 3-benzoylquinoline (164). [87] Scheme 38 Intramolecular [4ϩ2] cycloadditions of azaxylylenes generated under FVT conditions from N-alkylbenzoxazin-2-ones bearing a terminal double bond in an alkyl substituent proceed in low yields.…”

“…[87] With alkynes, such as ethynyl phenyl ketone, the initial cycloadduct 163 eliminates toluenesulfinic acid, resulting in 3-benzoylquinoline (164). [87] Scheme 38 Intramolecular [4ϩ2] cycloadditions of azaxylylenes generated under FVT conditions from N-alkylbenzoxazin-2-ones bearing a terminal double bond in an alkyl substituent proceed in low yields. [70,85] Such xylylenes mostly undergo [1,5]-sigmatropic hydrogen shifts, giving imines.…”

“…Scheme 39 An intramolecular DielsϪAlder reaction of aza-ortho-xylylene 169, generated from 168 and incapable of undergoing a [1,5]-hydrogen shift, gives the sultam 170 in moderate yield (Scheme 40). [87] Scheme 40…”

Decarboxylative cyclizations and cycloadditions of palladium-polarized aza-ortho-xylylenes

“…Thus, the product of Grignard addition was treated with potassium carbonate to ensure high-yielding cyclization 8. Finally, N -tosylation under standard conditions gave the desired starting material 9. Importantly, this process could be carried out without chromatographic purification of any intermediates.…”

“…4 However, these substrates give rise to aza- ortho -xylylene synthons ( C ) 5. The decarboxylation of vinyl benzoxazinones under conditions of palladium catalysis occurs at 25 °C and is thus significantly milder than thermal decarboxylation of benzoxazinones which typically requires temperatures near 200 °C 6. In addition, the aza- ortho -xylylene equivalents generated in the presence of palladium are more polarized than standard aza- ortho -xylylenes.…”