C₂-Symmetric Copper(II) Complexes as Chiral Lewis Acids. Catalytic Enantioselective Carbonyl−Ene Reactions with Glyoxylate and Pyruvate Esters

Abstract

The C 2 -symmetric complexes [Cu(S,S)-tert-butylbis(oxazolinyl)](SbF6)2 (2a), its bis(aquo) counterpart [Cu(S,S)-tert-butylbis(oxazolinyl)(H2O)2](SbF6)2 (4), and [Cu(S,S)-phenylbis(oxazolinyl)](OTf)2 (1c) have been shown to catalyze the enantioselective ene reaction between glyoxylate esters and various olefins. Monosubstituted, disubstituted, and trisubstituted olefins each react with ethyl glyoxylate in the presence of 0.2−10 mol % of catalysts 1, 2, and 4 to afford the ene products in good yield and enantioselectivity. Complex 2a has also been shown to catalyze the addition of 1,1-disubstituted olefins to methyl pyruvate in good yields (76−95%) and excellent enantioselectivies (≥98% ee). The synthetic utility of the glyoxylate−ene reaction was demonstrated by conversion of the resulting α-hydroxy ester into the corresponding methyl ester, free acid, Weinreb amide, and α-azido ester, all with no detectable racemization.

Stereoselective Assembly of a 1,3-Diene via Coupling between an Allenic Acetate and a (B)-Alkylborane: Synthetic Studies on Amphidinolide B1

“…23 The free alcohol was protected as its corresponding TBS ether and converted to the Weinreb amide 21. In parallel, vinyl iodide 23 was prepared from commercially available pentyn-1-ol 22 via two steps 24 in 50% overall yield.…”

Synthesis of Perhydrofuro[2,3‐b]furans from Isopentenyl Alcohol through Carbonyl‐Ene and Wacker‐Type Reactions

“…[12] Few reports deal with protected methallyl alcohol as the ene component, [13] whereas the carbonyl-ene reaction with isopentenyl alcohol has been seldom studied. [14] We wish to present herein a new and straight route towards the synthesis of functionalised 2-substituted perhydrofuro [2,3-b]furans involving the carbonyl-ene reaction of protected isopentenyl alcohol with activated enophiles, followed by deprotection and oxidation-acetalisation under Wacker-type [15] reaction conditions.…”

Enantioselective Carbonyl‐Ene Reactions of Trifluoropyruvate in Ionic Liquid via a Recyclable Indium(III)‐Pybox Complex

“…[3] The asymmetric carbonyl-ene reaction of trifluoropyruvate, [4] one type of ketone-ene reaction, is an effective methodology for constructing optically active tertiary homoallylic alcohols, containing a trifluoromethyl group, which are important building blocks for pharmaceuticals and agrochemicals. To our surprise, however, there are only few successful examples of asymmetric ketone-ene reactions [4,5] compared to the extensive studies of asymmetric aldehyde-ene reactions. [6] Thus far, the ketoneene reaction still remains as a challenge.…”