Formal enantioselective Michael addition with umpolung of reactivity.
By a sequence comprising asymmetric hydroboration, boron-zinc exchange, and transmetalation with copper, allylations, alkynylations, and allenylations of unsaturated ketals or acetals can be performed with good enantioselectivities (see scheme, (-)-IpcBH2 =(-)-isopinocampheylborane, TMS=Me3 Si). The products correspond to a formal Michael addition with inversion of polarity.
Ludwig-Maximilians-Universität München Department of Chemie Butenandtstrasse 5-13, 81377 München, Germany, Fax: (+49) 89-2180-7680.
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E
Hupe
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P
Knochel
Michael addition; asymmetric synthesis; hydroboration; umpolung; zinc