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Monday, June 9, 2014
Douglass F. Taber
University of Delaware

Organic Functional Group Protection

Dithianes such as 1 are readily prepared, from the corresponding ketone or by alkylation. Masayuki Kirihara of the Shizuoka Institute of Science and Technology developed (Tetrahedron Lett. 2013, 54, 5477. ) an oxidative method for the deprotection of 1 to 2. Konrad Tiefenbacher of the Technische Universität München devised (J. Am. Chem. Soc. 2013, 135, 16213. ) a hexameric resorcinarene capsule that selectively catalyzed the hydrolysis of the smaller acetal 3 in the presence of a longer chain acetal.

David J. Gorin of Smith College reported (J. Org. Chem. 2013, 78, 11606. ) the methylation of an acid 5 using dimethyl carbonate as the donor. Two peroxide-based methods (J. Org. Chem. 2013, 78, 9898, ; Org. Lett. 2013, 15, 3326, ) for carboxylic acid methylation (not illustrated) were also recently described. Hisashi Yamamoto of the University of Chicago showed (Angew. Chem. Int. Ed. 2013, 52, 7198. ) that the "supersilyl" ester 8 was stable enough to be deprotonated and alkylated, but was easily removed.

Michal Szostak and David J. Procter of the University of Manchester uncovered (Angew. Chem. Int. Ed. 2013, 52, 7237. ) the remarkable cleavage of a C-N bond in an amide 9, leading to the secondary amide 10. This could offer an alternative strategy for difficult to hydrolyse amides. Richard B. Silverman of Northwestern University described (J. Org. Chem. 2013, 78, 10931. ) improved protocols for the formation and removal of the N-protecting 2,5-dimethylpyrrole 11. Huanfeng Jiang of the South China University of Technology showed (Chem. Commun. 2013, 49, 6102. ) that an arenesulfonamide 14 can be prepared by oxidation of the corrresponding sodium arenesulfinate. Douglas Klumpp of Northern Illinois University prepared (Tetrahedron Lett. 2013, 54, 5945. ) sulfonamides (not illustrated) by combining a sulfonyl fluoride with a silyl amine. K. Rajender Reddy of the Indian Institute of Chemical Technology developed (Chem. Commun. 2013, 49, 6686. ) a new route to a urea 17, by oxidative coupling of an amine 15 with a formamide 16.

Davir González-Calderón and Carlos Gonzáles-Romero of the Universidad Autónoma del Estado de México used (Tetrahedron Lett. 2013, 54, 5130. ) CuSO4 hydrate in methanol to remove the t-butyldimethylsilyl ether of 18 in the presence of triisopropylsilyl (TIPS) and diphenyl t-butylsilyl (TBDPS) ethers. Shoji Akai and Ken-ichi Sato of Kanagawa University developed (J. Org. Chem. 2013, 78, 8802. ) a nitrosative protocol for the cleavage of the N-phenylcarbamoyl protecting group of 20. Shino Manabe and Yukishige Ito of RIKEN showed (Chem. Commun. 2013, 49, 8332. ) that the sulfonylcarbamate protecting group of 22 was stable to strong base, but was smoothly removed under mild conditions. Hirokazu Urabe of the Tokyo Institute of Technology reported (Adv. Synth. Catal. 2012, 354, 3480. ) the oxidation of the benzyl ether 24 to 25. The oxidized product 25 is primed for alcohol deprotection under either hydrolytic or mildly reductive conditions.

Pavel Nagorny of the University of Michigan employed (Angew. Chem. Int. Ed. 2013, 52, 12932. ) an enantiomerically-pure phosphoric acid to effect regioselective protection of 26. Under simple acidic conditions, the other regioisomer dominated. Kian Tan, now at Novartis, designed (Nature Chem. 2013, 5, 790. ) an enantiomerically-pure imidazole to catalyze selective acylation. The selectivity with the arabinose derivative 29 was particularly striking. Under catalysis by N-methyl imidazole, mesylation was predominantly at position 2, as illustrated. With the (-) catalyst, mesylation was at position 3, and with the (+) enantiomer of the catalyst mesylation occurred selectively at position 4.

D. F. Taber, Org. Chem. Highlights 2014, June 9.
URL: https://www.organic-chemistry.org/Highlights/2014/09June.shtm