Fast Chemistry by Microwave Heating : First Descriptions of Highly Enantioselective Microwave Protocols for Metal Catalysis; First Descriptions of in-situ Gas Generation for Fast Combinatorial Microwave Chemistry
Abstract: Microwave heating was applied to different palladium-catalyzed allylic substitution reactions. The use of various nucleophiles demonstrated C-, N-, O- and S- nucleophilicity. High yields and stereopurities of the corresponding alkyls, amides, ethers and sulfones were afforded after only 30 – 120 s of heating. The sensitive stereocontrol induced by the catalyst and the catalytic activity were sustained (88 to > 99 % enantiomeric excess (ee) ) despite high temperatures (up to 215oC) and forced conditions. Rapid molybdenum-catalyzed allylic alkylation was undertaken utilizing microwave heating. This formerly troublesome catalysis was developed into a simple, fast and convenient protocol. The protocol was employed in a structure-activity investigation for optimizing catalytic activity. An electron-rich environment with low steric restriction around the catalyzing molybdenum improved catalytic activity as well as induced stereoselectivity (> 99 % ee).A new methodology was developed for performing carbon monoxide reactions without the use of gaseous carbon monoxide from an external source. Solid metal carbonyls of low toxicity were utilized for in situ liberation of carbon monoxide directly into the reaction mixture. The methodology was applied to the combinatorial microwave-assisted synthesis of a small sized substance library of amidated HIV-1 protease inhibitors.
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