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2001
C-C bond formation
C-C bond formation
O 0282
Strictly Regiocontrolled α-Monosubstitution of Cyclic Carbonyl Com16 - 075 pounds with Alkynyl and Alkyl Groups via Pd-Catalyzed Coupling of
Cyclic α-Iodoenones with Organozincs. — Optimized conditions for the
palladium-catalyzed regiocontrolled α-alkylation and α-alkynylation of cyclic
α-iodoenones are presented. Reaction of iodoenone (II) with in situ generated
alkynylzinc reagents in the presence of Pd(dba)2 ·P(2-furyl)3 proceeds smoothly
to give α-alkynylated cyclohexenones (III). This reaction is successfully applied
to the preparation of Tbs-protected harveynone and tricholomenyn A (VI).
The α-alkylation reaction proceeds similarly with organozinc reagents in the
presence of PdCl2 (PPh3 )2 , but good yields are obtained only for primary
alkylzinc derivatives. s-Butylzinc reagent (X) affords only the n-butylated
enone (IXa). α-Allylation as well as α-propargylation does not proceed in
the expected way, instead 1,2-addition to the carbonyl group is observed [cf.
(XVIII)]. — (NEGISHI, EI-ICHI; TAN, ZE; LIOU, SHOW-YEE; LIAO,
BAIQIAO; Tetrahedron 56 (2000) 52, 10197-10207; Brown and Wetherill Lab.
Chem., Purdue Univ., West Lafayette, IN 47907, USA; EN)
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