A divergent synthesis of optically active quaternary Δ - and Δ -dehydro prolines is developed based on the first catalytic enantioselective conjugate addition of α-substituted isocyano(thio)acetates to vinyl ketones that is general for both α-aryl and α-alkyl isocyano(thio)acetates. The new tetrasubstituted C-N stereocenter is formed without the need of any metal salt due to a bifunctional tertiary amine/squaramide catalyst, featuring a bulky polyaryl sidearm and an unusually short squaramide diamide H⋅⋅⋅H interatomic distance in the solid state.
An effective asymmetric route to functionalized 1,6- and 1,7-enynes has been developed based on a direct cross-aldol reaction between ω-unsaturated aldehydes and propargylic aldehydes (α,β-ynals) promoted by combined α,α-dialkylprolinol ether/Brønsted acid catalysis. This synergistic activation strategy is key to accessing the corresponding aldol adducts with high stereoselectivity, both enantio- and diastereoselectivity. The aldol reaction also proceeds well with propargylic ketones (α,β-ynones) thus enabling a stereocontrolled access to the corresponding tertiary alcohols. The utility of these adducts, which are difficult to prepare through standard methodology, is demonstrated by their transformation into trisubstituted bicyclic enones using standard Pauson-Khand conditions.
Catalytic Enantioselective Quick Route to Aldol-Tethered 1,6-and 1,7-Enynes from -Unsaturated Aldehydes. -Direct cross-aldol reaction between -unsaturated aldehydes and propargylic aldehydes is developed to yield functionalized 1,6-and 1,7-enynes and the conversion of these products to bicyclic cyclopentenone derivatives by Pauson-Khand reaction is demonstrated. -(GARCIA, J. M.; ODRIOZOLA, J. M.; RAZKIN, J.; LAPUERTA, I.; ODRIOZOLA, A.; URRUZUNO, I.; VERA, S.; OIARBIDE, M.; PALOMO*, C.; Chem. -Eur. J. 20 (2014) 47, 15543-15554, http://dx.
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