Decomposition of 2-diazo-1,3-diketones: Stereocontrol of the mechanism.
摘要:
Complete ''inversion'' of alkyl to aryl migratory tendency in Wolff rearrangement of diazodiketones with Z,Z-conformation was revealed by comparing decomposition behavior of the planar diazo tetralindione with its twisted acyclic analogues. Dramatic change in regioselectivity of this process was accompanied by the appearance of X-H insertion products in the reaction mixture. These data suggest that on the way from planar cyclic to highly skewed acyclic aroylacyldiazomethanes concerted Wolff rearrangement turns into a carbenic process.
Increasing steric hindrance in β-keto carboxylic acids leads to an increasing kinetic stability towards decarboxylation, till systems are reached which are completely stable at room temperature. Simultaneously the tautomeric equilibrium is changed in favour of the (Z)-enol, and finally in favour of the (E)-configurated enol.