An enantio-, diastereo-, regio-, and chemoselective phosphine-catalyzed β,γ-umpolung domino reaction of allenic esters with dienones has been developed for the first time. The designed sequence, involving oxy-Michael and Rauhut-Currier reactions, produced highly functionalized tetrahydrobenzofuranones, bearing a chiral tetrasubstituted stereogenic center, in up to 96 % ee.
A highly
atom-economical, chemoselective, and stereoselective Lewis
base (LB)-catalyzed dual umpolung domino Michael reaction between
cyclohexadienones and alkynyl esters has been developed. PPh3, as a LB catalyst, afforded either the hydroindole-2-carboxylates
or hydrobenzofuran-2-carboxylates 3 as a single diastereomer
in high yields (up to 89%). An obtained product could be easily transformed
to a (S*,S*,R*)-octahydroindole-2-carboxylic acid
((S*,S*,R*)-Oic) analogue.
Mixing of acryloylchloride, dienone 2, N,N-diisopropylethylamine with chiral organocatalyst 5a, which could simultaneously act as Brønsted and Lewis base catalysts, led to a one-pot amidation/Rauhut-Currier sequence, affording α-methylidene-γ-lactams 4. Catalyst 5a could be recovered and reused by acid/base extraction without any loss of catalytic activity in the stepwise protocol.
A highly enantioselective aza-Morita-Baylis-Hillman (aza-MBH) reaction of isatin-derived ketimines with acrolein was established using β-isocupreidine (β-ICD) or α-isocupreine (α-ICPN) as a chiral acid-base organocatalyst. The present protocol readily furnished (S) or (R)-aza-MBH adducts with a chiral tetrasubstituted carbon stereogenic center in up to 98% ee.
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