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, 1974-and Wills, Martin. (2012 Application of tethered ruthenium catalysts to asymmetric hydrogenation of ketones, and the selective Hydrogenation of aldehydes. Advanced Synthesis & Catalysis, 354 (13). pp. 2545-2555. Permanent WRAP url:http://wrap.warwick.ac.uk/55017 Copyright and reuse:The Warwick Research Archive Portal (WRAP) makes this work by researchers of the University of Warwick available open access under the following conditions. Copyright © and all moral rights to the version of the paper presented here belong to the individual author(s) and/or other copyright owners. To the extent reasonable and practicable the material made available in WRAP has been checked for eligibility before being made available. Copies of full items can be used for personal research or study, educational, or not-for profit purposes without prior permission or charge. Provided that the authors, title and full bibliographic details are credited, a hyperlink and/or URL is given for the original metadata page and the content is not changed in any way. Abstract. An improved method for the synthesis of tethered ruthenium(II) complexes of monosulfonylated diamines is described, together with their application to hydrogenation of ketones and aldehydes. The complexes were applied directly, in their chloride form, to asymmetric ketone hydrogenation, to give products in excess of 99% ee in the best cases, using 30 bar of hydrogen at 60 °C , and to the selective reduction of aldehydes over other functional groups.

In this update, the asymmetric homogeneous hydrogenation of a number of trisubstituted olefins utilizing the recently developed tube‐in‐tube gas‐liquid flow reactor is described. A number of chiral iridium‐ and rhodium‐based catalysts and other parameters such as pressure, solvent, temperature and catalyst loading were screened. The advantage of the flow set‐up for rapid screening and optimization of reaction parameters is illustrated. Furthermore, a comparative study using batch conditions aided in the optimization of the flow reaction set‐up. The set‐up was further modified to recycle the catalyst which prolonged catalytic activity.

In situ NMR and IR spectroscopy studies were carried out on the rearrangement of lithiated N‐benzyl‐N′‐aryl ureas, which involves N‐to‐C aryl transfer with retention of configuration. The IR spectroscopy studies revealed that initial benzylic lithiation was followed by migration of the aryl ring to yield a lithiated urea product without a detectable dearomatised intermediate. Similar results were obtained by NMR spectroscopy, but when 1,3‐dimethyl‐3,4,5,6‐tetrahydro‐2(1H)‐pyrimidinone (DMPU) was added to the solvent mixture, a transient dearomatised intermediate was detectable during migration of a 1‐naphthyl ring. DFT calculations highlight the importance of coordinated lithium cations, and their migration from one site to another, in the rearrangement. Rearrangement is initiated by migration of a solvated lithium cation from the anionic centre of the starting organolithium to a site close the adjacent phenyl ring, allowing retentive attack of the anionic centre on the more remote ring with movement of the solvated lithium cation to the remote ring stabilising the developing negative charge. A short‐lived spirocyclic intermediate is predicted to undergo elimination by loss of the urea substituent, completing the migration. Coordination of the carbonyl group to a second solvated lithium cation appears to be essential for this step. Calculated shifts for this intermediate when a 1‐naphthyl ring is migrating are consistent with the transient signals observed by NMR spectroscopy. Alternative pathways involving (1) invertive migration and (2) attack on the urea C=O group were also calculated and were found to require significantly higher energy transition states.

Atropisomeric biaryl pyridine and isoquinoline N-oxides were synthesized enantioselectively by dynamic kinetic resolution (DKR) of rapidly racemizing precursors exhibiting free bond rotation. The DKR was achieved by ketoreductase (KRED) catalyzed reduction of an aldehyde to form a configurationally stable atropisomeric alcohol, with the substantial increase in rotational barrier arising from the loss of a bonding interaction between the N-oxide and the aldehyde. Use of different KREDs allowed either the M or P enantiomer to be synthesized in excellent enantiopurity. The enantioenriched biaryl N-oxide compounds catalyze the asymmetric allylation of benzaldehyde derivatives with allyltrichlorosilane.

We report a new mode of reactivity displayed by lithiated O-benzyl carbamates carrying an N-aryl substituent: upon lithiation, the N-aryl group is transferred cleanly from N to C. An arylation of the carbamate results, providing a route to alpha,alpha-arylated secondary or tertiary alcohols. We also report density functional theory calculations supporting the proposal that arylation proceeds through a dearomatizing attack on the aromatic ring, a significantly lower energy pathway than the 1,2-acyl transfer observed with related N-alkyl carbamates.

Atropisomeric biaryls carrying ortho-hydroxymethyl and formyl groups were made enantioselectively by desymmetrisation of dialdehyde or diol substrates. The oxidation of the symmetrical diol substrates was achieved using a variant of galactose oxidase (GOase), and the reduction of the dialdehydes using a panel of ketoreductases. Either M or P enantiomers of the products could be formed, with absolute configurations assigned by time-dependent DFT calculations of circular dichroism spectra. The differing selectivities observed with different biaryl structures offer an insight into the detailed structure of the active site of the GOase enzyme.

The development of a stereoselective total synthesis of β-dihydroagarofuran 4 is described. This compound contains the same oxygenation pattern on its 'lower-rim' as found in the natural sesquiterpene (-)-euonyminol (1) and it is expected that the route described should be applicable to the synthesis of that complex natural product. (-)-Euonyminol is found as the core scaffold of a series of complex macrodilactone sesquiterpenoids isolated from the Celastraceae which possess interesting biological activities (e.g. anti-HIV activity). The synthetic route builds upon an epoxidative asymmetric desymmetrisation of meso-diallylic alcohol 10 that we have reported previously. It features a lactate Ireland-Claisen rearrangement to establish the quaternary stereocentre at C11 (27→28a) and an unusual dealkylative intramolecular epoxide-opening by the C11 methyl ether to establish the tetrahydrofuranyl C-ring of the β-dihydroagarofuran skeleton (35→36).