Aryloxide-facilitated catalyst turnover in enantioselective α,β-unsaturated acyl ammonium catalysis

The authors thank the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013) ERC grant agreement no. 279850 (A.D.S) and the EPSRC (EP/J018139/1, A.M.) for funding. A.D.S. thanks the Royal Society for a Wolfson Research Merit Award.A new general concept for α,β-unsaturated acyl ammonium catalysis is reported that uses p-nitrophenoxide release from an α,β-unsaturated p-nitrophenyl ester substrate to facilitate catalyst turnover. This method was used for the enantioselective isothiourea-catalyzed Michael addition of nitroalkanes to α,β-unsaturated p-nitrophenyl esters in generally good yield and with excellent enantioselectivity (27 examples, up to 79% yield, 99:1 er). Mechanistic studies identified rapid and reversible catalyst acylation by the α,β-unsaturated p-nitrophenyl ester, and a recently reported variable-time normalization kinetic analysis method was used to delineate the complex reaction kinetics.Publisher PDFPeer reviewe

Enantioselective synthesis of 2,3-disubstituted trans-2,3-dihydrobenzofurans using a Brønsted base/thiourea bifunctional catalyst

The research leading to these results (D-J.B.A.; C. F.) has received funding from the ERC under the European Union's Seventh Framework Programme (FP7/2007-2013) / ERC grant agreement n° 279850. ADS thanks the Royal Society for a Wolfson Research Merit Award.The diastereo- and enantioselective synthesis of 2,3-disubstituted trans-2,3-dihydrobenzofuran derivatives (15 examples, up to 96:4 dr, 95:5 er) via intramolecular Michael addition has been developed using keto-enone substrates and a bifunctional tertiary amine-thiourea catalyst. This methodology was extended to include non-activated ketone pronucleophiles for the synthesis of 2,3-disubstituted indane and 3,4-disubstituted tetrahydrofuran derivatives.PostprintPeer reviewe

Aryloxide-facilitated catalyst turnover in enantioselective α,β-unsaturated acyl ammonium catalysis

A new general concept for α,β-unsaturated acyl ammonium catalysis is reported that uses p-nitrophenoxide release from an α,β-unsaturated p-nitrophenyl ester substrate to facilitate catalyst turnover. This method was used for the enantioselective isothiourea-catalyzed Michael addition of nitroalkanes to α,β-unsaturated p-nitrophenyl esters in generally good yield and with excellent enantioselectivity (27 examples, up to 79% yield, 99:1 er). Mechanistic studies identified rapid and reversible catalyst acylation by the α,β-unsaturated p-nitrophenyl ester, and a recently reported variable-time normalization kinetic analysis method was used to delineate the complex reaction kinetics

Enantioselective synthesis of 2,3-disubstituted trans-2,3-dihydrobenzofurans using a Brønsted base/thiourea bifunctional catalyst

The diastereo- and enantioselective synthesis of 2,3-disubstituted trans-2,3-dihydrobenzofuran derivatives (15 examples, up to 96:4 dr, 95:5 er) via intramolecular Michael addition has been developed using keto-enone substrates and a bifunctional tertiary amine-thiourea catalyst. This methodology was extended to include non-activated ketone pronucleophiles for the synthesis of 2,3-disubstituted indane and 3,4-disubstituted tetrahydrofuran derivatives

Catalytic enantioselective synthesis of perfluoroalkyl-substituted β-lactones via a concerted asynchronous [2+2] cycloaddition : a synthetic and computational study

The research leading to these results (D.-J.B.A., T.H.W., A.D.S.) has received funding from the ERC under the European Union’s Seventh Framework Programme (FP7/2007-2013)/E.R.C. Grant Agreement No. 279850. A.D.S. thanks the Royal Society for a Wolfson Research Merit Award. We also thank the EPSRC UK National Mass Spectrometry Facility at Swansea University. P.H.Y.C. is the Bert and Emelyn Christensen professor of OSU, and gratefully acknowledges financial support from the Vicki & Patrick F. Stone family. P.H.Y.C., A.C.B., D.M.W. and B.G.Y. gratefully acknowledge support from the National Science Foundation (NSF CHE-1352663) and the computing infrastructure in part provided by the NSF Phase-2 CCI, Center for Sustainable Materials Chemistry (NSF CHE-1102637).The enantioselective preparation of a range of perfluoroalkyl-substituted β-lactones through an isothiourea (HyperBTM) catalysed reaction using symmetric anhydrides as ammonium enolate precursors and perfluoroalkylketones (RF = CF3, C2F5, C4F9) is reported. Following optimisation, high diastereo- and enantioselectivty was observed for β-lactone formation using C2F5- and C4F9-substituted ketones at room temperature (26 examples, up to > 95:5 dr and > 99:1 er), whilst −78 ˚C was necessary for optimal dr and er with CF3-substituted ketones (11 examples, up to > 95:5 dr and > 99:1 er). Derivatisation of the β-lactones through ring-opening, as well as a two-step conversion to give perfluoroalkyl-substituted oxetanes, is demonstrated without loss of stereochemical integrity. Density functional theory computations, alongside 13C natural abundance KIE studies, have been used to probe the reaction mechanism with a concerted asynchronous [2 + 2]-cycloaddition pathway favoured over a stepwise aldol-lactonisation process.Publisher PDFPeer reviewe

Catalytic enantioselective synthesis of perfluoroalkyl-substituted β-lactones via a concerted asynchronous [2+2] cycloaddition: a synthetic and computational study (crystallography data)

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