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Monday, November 8, 2010
Douglass F. Taber
University of Delaware

Functional Group Protection

Bekington Myrboh of North-Eastern Hill University reported (Tetrahedron Lett. 2010, 51, 2862. ) a convenient procedure for the oxidative removal of a 1,3-oxathiolane 1 or a 1,3-dithiolane. Sang-Gyeong Lee and Yong-Jin Yoon of Gyeongsang National University developed (J. Org. Chem. 2010, 75, 484. ) the pyridazin-3(2H)-one 4 for the microwave-mediated deprotection of an oxime 3. Dario M. Bassani of Université Bordeaux 1 and John S. Snaith of the University of Birmingham devised (J. Org. Chem. 2010, 75, 4648. ) a procedure for the facile preparation of esters such as 6. Brief photolysis (350 nm) returned the parent carboxylic acid 7.

Craig M. Williams of the University of Queensland prepared (Tetrahedron Lett. 2010, 51, 1158. ) the trithioorthoester 8 by iterative opening of epichlorohydrin. He found that the keto ester 9 could be efficiently released by Hg-mediated hydrolysis.

Masatoshi Mihara of the Osaka Municipal Technical Research Institute established (Synlett 2010, 253. ) that even very congested alcohols such as 10 could be acetylated by acetic anhydride containing a trace of FeCl3. Colleen N. Scott, now at Southern Illinois University, developed (J. Org. Chem. 2010, 75, 253. ) a convenient procedure for the preparation of the hydridosilane 13, that on Mn catalysis added the alcohol 12 to make the unsymmetrical bisalkoxysilane 14. Sabine Berteina-Raboin of the Université d’Orléans found (Tetrahedron Lett. 2010, 51, 2115. ) that NaBH4 in EtOH cleanly removed the chloroacetates from 15. Both other esters and silyl ethers were stable under these conditions. Ram S. Mohan of Illinois Wesleyan University established (Tetrahedron Lett. 2010, 51, 1056. ) that Fe(III) tosylate in methanol selectively removed the alkyl silyl ether from 17 without affecting the aryl silyl ether.

Alakananda Hajra and Adinath Majee of Visva-Bharati University effected (Tetrahedron Lett. 2010, 51, 2896. ) formylation of an amine 19 by heating with commercial 85% formic acid as the solvent in a sealed tube at 80°C. Although both primary and secondary amines could be efficiently formylated, the primary amines were much more reactive. Doo Ok Jang of Yonsei University found (Tetrahedron Lett. 2010, 51, 683. ) that the conveniently-handled CF3CCO2H (the acid chloride is a gas) could be activated in situ, to selectively convert 22 into 24. The importance of trifluoroacetamides was underscored by the report (Angew. Chem. Int. Ed. 2010, 49, 1850. ) from Paola Rota of the University of Milan that 25 could be acylated with an acid chloride. The trifluoroacetyl was then removed by mild hydrolysis, completing the protecting group exchange without jeopardizing the esters.

Chuangxing Guo of Pfizer/San Diego observed (Tetrahedron Lett. 2010, 51, 2909. ) that in situ coupling of the sulfamyl chloride derived from 27 with 28 in the presence of pyridine as the base gave low yields of the coupled product, accompanied by a substantial amount of the undesired primary mixed sulfamide. Using 3,5-lutidine as the base gave clean conversion to 29.

D. F. Taber, Org. Chem. Highlights 2010, November 8.