Sunday, December 18, 2011

Ligand-Accelerated Cross-Coupling of C(sp2)–H Bonds with Arylboron Reagents

Keary M. Engle, Peter S. Thuy-Boun, Michael Dang, and Jin-Quan Yu
J. Am. Chem. Soc., 2011, 133, 18183–18193

A palladium catalyzed C–H functionalization between Molander's arylboronate reagents and phenylacetic acid derivatives was demonstrated. From extensive screening, this synthetic method was found to be efficacious utilizing Ac-Ile-OH as the ligand and Ag2CO3 as the oxidant. As a result, a high yielding and experimentally straightforward procedure has evolved into a useful cross-coupling protocol between arylacetic acid derivatives and aryltrifluoroborates.  The authors also found that this ligand accelertated process has superb functional group tolerance and may also be beneficial when applied to catalytic cross-coupling conditions under an oxygen atmosphere thus providing alternative "Green" conditions for this biaryl transformation.

Friday, December 2, 2011

A Highly Enantio- and Diastereoselective Molybdenum-Catalyzed Asymmetric Allylic Alkylation of Cyanoester

10 mol% Mo(CO)6, 15 mol% ligand, 10 mol% NaH, BSA, THF, 60 deg C
99% yield, 20/1 Branched/Linear, 11/1 dr, 97% ee

Barry M. Trost, John R. Miller, and Christopher M. Hoffman, Jr
J. Am. Chem. Soc.2011133, 8165–8167

Summary: An efficacious Mo-catalyzed enantioselective allylation of various cyanoester nucleophiles provided a number of highly functionalized branched cyanoesters containing a quaternary carbon stereocenter.  This synthetic method generates the desired allylic cyanoesters products with high yield, chemoselectivity, diastereoselectivity and enantioselectivity.

Tuesday, November 29, 2011

Reaction Development and Mechanistic Study of a Ruthenium Catalyzed Intramolecular Asymmetric Reductive Amination en Route to the Dual Orexin Inhibitor Suvorexant (MK-4305)

Neil A. Strotman, Carl A. Baxter, Karel M. J. Brands, Ed Cleator, Shane W. Krska, Robert A. Reamer, Debra J. Wallace, Timothy J. Wright

Summary: Suvorexant (MK-4305) is a potent dual Orexin antagonist under development for the treatment of sleep disorders at Merck. The key transformation is an intramolecular asymmetric Ru-catalyzed transfer hydrogenation (using a modified Noyori RuCl(p-cymene)(DPEN) complex) of an in-situ generated cyclic imine resulting in the formation of the desired diazepane in 97% yield and 94.5% ee. Mechanistic studies have revealed that CO2 (derived from the formic acid) has pronounced effect on reaction outcome.  Studies have determined that the efficiency of the Ru-catalyst, the composition of the resulting amine (i.e. carbamate formation), and the reaction kinetics are mediated by the amount of CO2 generated during the reaction. The efficiency of the reductive-amination can be enhanced by either purging of the CO2 or by trapping the thus formed nucleophilic secondary amines.


Sunday, March 8, 2009

Rhodium-Catalyzed Reductive Cleavage of Carbon−Cyano Bonds with Hydrosilane: A Catalytic Protocol for Removal of Cyano Groups

Mamoru Tobisu, Ryo Nakamura, Yusuke Kita and Naoto Chatani
J. Am. Chem. Soc., 2009, 131, 3174–3175

Summary: Recently, transition metal activation of the C-CN bond has been an area of intense synthetic activity. Much of the previous work has been centered around Ni(0) mediated C-C bond formation. The Chatani group has developed a rhodium-catalyzed hydrosilane mediated reductive cleavage of the C−CN bond. The reaction has a large synthetic scope including decyanation of aryl- and alkyl nitriles. Additionally, the reaction has a very good functional group tolerence and can be performed in the presence of ester, ether, amino and amide groups. This synthetic method was also demonstrated in several examples where a cyano group was present as a removable ortho-directing group (via a C-H functionalization process).

Saturday, March 7, 2009

Efficient Boron−Copper Additions to Aryl-Substituted Alkenes Promoted by NHC−Based Catalysts. Enantioselective Cu-Catalyzed Hydroboration Reactions

Yunmi Lee and Amir H. Hoveyda
J. Am. Chem. Soc., 2009, 131, 3160–3161

Summary: This paper describes the development of a Cu-catalyzed formal hydroboration of olefinic substrates (styrene derivatives). The reaction is highly regio and stereoselective affording the organoboron products in moderate to high yield. The reaction utilizes a copper NHC complex (0.5-7.5 mol%) and pinacolatoboron as the boron source. In the asymmetic variant the er's range from 86/14 to 99/1.

Sunday, May 6, 2007

Rhodium-Catalyzed Asymmetric Synthesis of 3,3-Disubstituted 1-Indanones

Ryo Shintani, Keishi Takatsu, Tamio Hayashi

Angewandte Chemie International Edition; 2006, 46, 3537-3737
DOI: 10.1002/anie.200700226

Summary: Chiral indanones that are difficult to obtain by other synthetic methods can be prepared via an enantioselective addition of aryl boronates to aryl alkynyl ketones. The resulting substituted indanones arrive from a tandem Rh-catalyzed C-H functionalization-cyclization sequence. This reaction utilizes a rhodium catalyst system with the asymmetric induction originating from a chiral bisphosphine ligand.

Saturday, May 5, 2007

Palladium-Catalyzed Benzene Arylation: Incorporation of Catalytic Pivalic Acid as a Proton Shuttle and a Key Element in Catalyst Design

Marc Lafrance and Keith Fagnou
J. Am. Chem. Soc., 2006, 128, 16496 -16497
Summary: C-H activation processes represent an important area of synthetic exploration since the starting materials required are less functionalized and potentially less expensive. A Pd-pivalic acid co-catalyst system has been utilized in the direct arylation of benzene and aryl bromides. Experimental and computational studies indicate that the pivalate anion is a key component in the palladation/C-H bond breaking event. Additionally, aryl chorides and iodides were found to be poor substrates.

8 examples: 55-85%