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2005
Rearrangements
O 0140
Synthetic Stitching with Silicon: Geminal Alkylation—Hydroxylation of Alkynyl
Compounds. — A new three-step synthesis of β-carbonyl-substituted
12- 047 Carbonyl
tertiary alcohols from α,β-alkynyl ketones and esters is reported. In the first step
of the approach alkynyl esters and ketones (I) are selectively hydrosilylated to
(Z)-β-silyl-enones and enoates. With a variety of substituted silanes high yields and
Z/E selectivities of 7:1 to >20:1 are obtained. Subsequent one-pot C-C bond formation
by Si→C migration followed by silane oxidation affords the desired β-carbonyl-substituted tertiary alcohols. The 1,2-migration of a variety of groups like phenyl, benzyl,
2-furanyl and allyl is demonstrated. Methyl groups on silicon are not transferred. Vinyl
silanes with γ-chiral centers, cf. (IIId), afford the corresponding tertiary alcohol with
diastereoselectivity of up to >20:1, however a dependence of diastereoselectivity on the
water content of the reaction medium and on the acid derivative of the vinylsilane is
found. The diastereoselectivity of ester substrates like (VII) is low, however a change
to acyl oxazolidinones affords products (X) with high yield and control of diastereoselectivity. — (TROST*, B. M.; BALL, Z. T.; J. Am. Chem. Soc. 126 (2004) 43,
13942-13944; Dep. Chem., Stanford Univ., Stanford, CA 94305, USA; Eng.) —
Bartels
2005
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