A highly enantioselective transformation catalyzed by chiral (acyclic diaminocarbene)gold(I) complexes is reported. The enantioselective synthesis of 2-substituted chromenyl pivalates from racemic phenol-substituted propargyl pivalates was developed. Rearrangement of the substrates in the presence of cationic gold gave allene intermediates, whose cyclization resulted in formation of enantioenriched product through a dynamic kinetic asymmetric transformation.
A chiral anion phase-transfer system for enantioselective halogenation is described. Highly insoluble, ionic reagents were developed as electrophilic bromine and iodine sources, and application of this system to o-anilidostyrenes afforded halogenated 4H-3,1-benzoxazines with excellent yield and enantioselectivity.
Chiral (Acyclic diaminocarbene)gold(I)-Catalyzed Dynamic Kinetic Asymmetric Transformation of Propargyl Esters. -The title reaction of phenol-substituted propargyl pivalates (I) or (III) proceeds via a formal [3,3] sigmatropic rearrangement followed by a 6-endo-trig cyclization to give enantioenriched 2-substituted chromenyl pivalates. Phenol ether analogues (V) afford 2,3-disubstituted chromenyl pivalates (VI) which are formed by an additional 1,3-migration of the ether group to a carbon atom. -(WANG, Y.-M.; KUZNIEWSKI, C. N.; RAUNIYAR, V.; HOONG, C.; TOSTE*, F. D.; J. Am. Chem. Soc. 133 (2011) 33, 12972-12975, http://dx.
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