Read e-book online Aminomethylenemalonates and Their Use in Heterocyclic PDF

By Alan R. Katritzky (Eds.)

ISBN-10: 0120207540

ISBN-13: 9780120207541

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195 Although N ,N -bis[3,5-bis(trifluoromethyl)phenyl]thiourea is achiral, its addition to aldols catalysed by l-proline (61) enhances the diastereo- and enantio-selectivities (up to 94 and >99%), via formation of a 1 : 1 host:guest complex. The complex is proposed to involve hydrogen bonding between the proline oxygens and the thiourea N−Hs, driven by the use of non-polar solvent. 196 4-Substituted cyclohexanones have been desymmetrized with high diastereo- and enantio-selectivities via a simple direct aldol reaction catalysed by l-proline (61).

For example, ethyl benzoylacetate (PhCOCH2 CO2 Et) reacts with benzylideneacetone (PhCH=CHCOMe) to yield enone (89). 339 A diarylprolinol TMS ether with heavy aromatic buttressing catalyses a tandem Michael addition–Wittig reaction of trans-enals with (3-carboxy-2oxopropylidene)-triphenylphosphorane (Ph3 P=CHCOCH2 CO2 −t-Bu) to yield cyclohexenone esters with 98% de and 99% ee. 340 An intramolecular Rauhut–Currier reaction creates a C−C bond between appropriately tethered Michael acceptors. A new enantioselective version (90 → 91) uses proline-derived catalysts to form electron-rich dienamines as key intermediates.

66), from benzaldehyde]. 227 t-Butyldimethylsilyl triflate, in combination with triethylamine, provides dual activation catalysis for intramolecular alkynylogous Mukaiyama aldol reaction of bicyclic alkanones tethered to alkynyl esters. 229 BINAPO, a chiral phosphine oxide, catalyses enantioselective direct aldols. 231 Enantioselective addition of O,O-ketene silyl acetals (derived from simple esters) to α-keto esters has been achieved using copper(II)–bis(oxazoline)complexes, dispensing with the need for the thioesters used in the Evans aldol.

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Aminomethylenemalonates and Their Use in Heterocyclic Synthesis by Alan R. Katritzky (Eds.)


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