Functional Group Interconversion

Chaozhong Li of the Shanghai Institute of Organic Chemistry reported (J. Am. Chem. Soc. 2012, 134, 10401) the silver nitrate catalyzed decarboxylative fluorination of carboxylic acids, which shows interesting chemoselectivity in substrates such as 1. A related decarboxylative chlorination was also reported by Li (J. Am. Chem. Soc. 2012, 134, 4258). Masahito Ochiai at the University of Tokushima has developed (Chem. Commun. 2012, 48, 982) an iodobenzene-catalyzed Hofmann rearrangement (e.g., 3 to 4) that proceeds via hypervalent iodine intermediates. The dehydrating agent T3P (propylphosphonic anhydride), an increasingly popular reagent for acylation chemistry, has been used (Tetrahedron Lett. 2012, 53, 1406) by Vommina Sureshbabu at Bangalore University to convert amino or peptide acids such as 5 to the corresponding thioacids with sodium sulfide. Jianqing Li and co-workers at Bristol-Myers Squibb have shown (Org. Lett. 2012, 14, 214) that trimethylaluminum, which has long been known to effect the direct amidation of esters, can also achieve the direct coupling of acids and amines, such as in the preparation of amide 8. The propensity of severely hindered 2,2,6,6-tetramethylpiperidine (TMP) amides such as 9 to undergo solvolysis at room temperature has been shown (Angew. Chem. Int. Ed. 2012, 51, 548) by Guy Lloyd-Jones and Kevin Booker-Milburn at the University of Bristol. The reaction proceeds by way of the ketene and is enabled by sterically induced destabilization of the usual conformation that allows conjugation of the nitrogen lone pair with the carbonyl. Matthias Beller at Universität Rostock has found (Angew. Chem. Int. Ed. 2012, 51, 3905) that primary amides may be transamidated via copper(II) catalysis. The conditions are mild enough that an epimerization-prone amide such as 11 undergoes no observable racemization during conversion to amide 13. A photochemical transamidation has been achieved (Chem. Sci. 2012, 3, 405) by Christian Bochet at the University of Fribourg that utilizes 385-nm light to activate a dinitroindoline amide in the presence of amines such as 15, which produces the amide 16. Notably, photochemical cleavage of the Ddz protecting group occurs at a shorter wavelength of 300 nm.