52nd International Chemistry Olympiad, Istanbul, TURKEY
Preparatory problems: THEORETICAL
Problem 5. ArndtโEistert Homologation Fritz Georg Arndt (6 July 1885โ8 December 1969) was a German chemist who had a great influence on the development of chemistry in Turkey. He was employed for two decades of his professional life at Istanbul University in two distinct periods. He discovered the ArndtโEistert synthesis with Bernd Eistert. The ArndtโEistert synthesis is the chemical reaction for onecarbon homologation (i.e. the conversion of RCO2H to RCH2CO2H) of carboxylic acids and is called the homologation process. In the ArndtโEistert homologation, the key step is the Wolff rearrangement of diazoketones to ketenes, which can be achieved thermally, photochemically, or by silver (I) catalysis. The reaction is conducted in the presence of nucleophiles such as water, alcohols, or amines to capture the ketene intermediate to yield carboxylic acids, esters, or amides, respectively. In this problem, synthesis of indolizidine alkaloids is studied.
5.1. As depicted in the scheme below, the synthesis of indolizidines 167B and coniceine could be easily and concisely achieved from ๏ข๏ฌ๏ง-unsaturated ester B. The key step (A โ B) is the Wolff rearrangement. Compound C has a lactam core, which is a bicyclic heterocycle containing a six-membered ring fused to a saturated five-membered ring, one of the bridging atoms being nitrogen. Draw the structures of AโD without any stereochemical detail.
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