An effective and straightforward approach to the synthesis of 4H-3,1-benzoxazines 3 and 4, quinazolin-2-ones 5, and quinoline-4-one derivatives 6 and 7 is provided by palladium-catalyzed cyclization-alkoxycarbonylation of variously substituted 2-(trimethylsilanyl)ethynylaniline amide or urea derivatives 2. Reactions are carried out in 7:1 MeCN/MeOH at 65 or 75 °C in the presence of catalytic amounts of 10% Pd/C in conjunction with Bu4NI and KF and under 2.4 MPa of a 3:1 mixture of CO and air. Anti and syn 6-exo-dig cyclization modes account for the formation of the two stereoisomers. Isomerization of the vinylpalladium intermediate may occur as well. Formation of a double carbonylation product 7r and of a gem-dimethoxycarbonylation product 6s, whose structures have been determined by X-ray diffraction analysis, is justified through an unusual type of rearrangement.
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|Titolo:||SYNTHESIS OF 4H-3,1-BENZOXAZINES, QUINAZOLIN-2-ONES AND QUINOLINE-4-ONES BY PALLADIUM-CATALYZED OXIDATIVE CARBONYLATION OF 2-ETHYNYLANILINE DERIVATIVES|
|Data di pubblicazione:||2004|
|Appare nelle tipologie:||1.1 Articolo in rivista|