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 coworkers 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 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. A fundamentally orthogonal approach to amide synthesis has been developed (Angew. Chem. Int. Ed. 2012, 51, 5683. ) by Gary Molander at the University of Pennsylvania and Jeff Bode at the ETH Zürich, which utilizes acyltrifluoroborates such as 17 and O-benzoyl hydroxylamines (e.g. 18) as coupling partners. The procedure is rapid and mild and remarkably occurs in aqueous t-BuOH solution.
Yoshito Kishi at Harvard University reported (Org. Lett. 2012, 14, 2262. ) an optimized procedure for the conversion of m-fluorophenylsulfones to the corresponding alcohols, a process utilized toward the synthesis of a building block of the complex molecule E7389 (cf. 20 to 21). A catalytic Appel reaction for alcohol chlorodehydration has been achieved (J. Org. Chem. 2011, 76, 6749. ) by Ross Denton at the University of Nottingham. Whereas catalytic triphenylphosphine oxide in the presence of oxalyl chloride leads to chloride products, the addition of LiBr to this mixture produces alkyl bromides, such as 23. The team of Takashi Ohshima at Kyushu University and Kazushi Mashima at Osaka University has accomplished (Angew. Chem. Int. Ed. 2012, 51, 150. ) the first direct amination of allylic alcohols with ammonia using platinum catalysis (e.g. 24 to 25), while Magnus Rueping at RWTH Aachen University reported (Org. Lett. 2012, 14, 768. ) a silver catalyzed azidation of allylic alcohols (e.g. 26 to 27).
An unusual copper catalyzed rearrangement of O-propargylic alkylaldoximes to generate oxiranyl N-alkenylimines (e.g. 28 to 29) has been disclosed (Org. Lett. 2012, 14, 206. ) by Itaru Nakamura at Tohoku University. Xiaodong Shi at West Virginia University found (J. Am. Chem. Soc. 2012, 134, 9012. ) that a triazole gold complex efficiently effects the hydration of propargylic acetates without epimerization, as in the conversion of 30 to 31. Evidence in support of the requirement of silver ions for the catalytic activity of other gold complexes was provided, demonstrating an important "silver effect" in gold(I) catalysis.