Written by: Dr. Sharbil J. Firsan
A new twist on the Hiyama cross-coupling reaction has recently been reported by Alacid and Najera. It features a ligandless, Pd-catalyzed cross-coupling that is carried out with aqueous sodium hydroxide as promoter and tetra-n-butylammonium bromide (TBAB) as additive at 120 oC under conventional or microwave heating. Good yields, stereoselectivities, low catalyst loadings, and ease of recovery of the Pd catalyst are characteristics of this reaction protocol.

Alacid, E.; Najera, C. J. Org. Chem. 2008, 73, 2315. See also Denmark, S. E.; Ober, M. H. Aldrichimica Acta 2003, 36, 75.
Written by: Dr. Sharbil J. Firsan
Dennis Hall and co-workers have recently disclosed the remarkable ability of ortho-bromo- and ortho-iodophenylboronic acids, [2-BrC6H4B(OH)2] and [2-IC6H4B(OH)2], to catalyze the direct amidation of free carboxylic acids with amines and the Diels–Alder reaction of free alpha,beta-unsaturated carboxylic acids with simple dienes. The noteworthy features of this discovery are:

Al-Zoubi, R. M.; Marion, O.; Hall, D. G. Angew. Chem., Int. Ed. 2008, 47, 2876. For selected recent reviews on organocatalysis, see: (a) Longbottom, D. A.; Franckevicius, V.; Kumarn, S.; Oelke, A. J.; Wascholowski, V.; Ley, S. V. Aldrichimica Acta 2008, 41, 3. (b) Lelais, G.; MacMillan, D. W. C. Aldrichimica Acta 2006, 39, 79.
Written by: Dr. Sharbil J. Firsan
Bolshan and Batey recently reported the copper-catalyzed, stereoselective cross-coupling of amides with potassium alkenyltrifluoroborates, leading to high yields of the corresponding enamides, which are valuable synthetic intermediates and important structural features in many natural products. Under optimized conditions, this reaction offers the following advantages over other enamide syntheses:

Bolshan, Y.; Batey, R. A. Angew. Chem., Int. Ed. 2008, 47, 2109.
Written by: Dr. Sharbil J. Firsan
A highly enantioselective and organocatalytic Michael addition of a-substituted aldehydes to nitroethylene has been reported by Gellman and co-workers.1,2 The metal-free catalyst system consists of (S)-diphenylprolinol silyl ether as the catalyst (2 mol %) and 3-nitrobenzoic acid as the co-catalyst (20 mol %). When followed by NaBH4 reduction of the aldehyde group of the addition product, the method leads to beta-substituted delta-nitrobutanols in excellent yields and enantioselectivities. In turn, these butanols can be readily converted into the corresponding N-protected gamma2-amino acids—important building blocks for gamma-peptides and heterogeneous-backbone foldamers—by a short and operationally simple sequence of hydroxyl group oxidation, nitro group reduction, and amino group protection.

(1) Chi, Y.; Guo, L.; Kopf, N. A.; Gellman, S. H. J. Am. Chem. Soc. 2008, 130, ASAP. (2) For a recent review on organocatalytic conjugate additions utilizing pyrrolidinyltetrazoles as organocatalysts, see Longbottom, D. A.; Franckevicius, V.; Kumarn, S.; Oelke, A. J.; Wascholowski, V.; Ley, S. V. Aldrichimica Acta 2008, 41, 3.
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