SmI2-Mediated Radical Cyclizations Directed by a C−Si Bond
摘要:
The use of a silicon stereocontrol element in cyclobutanol and cyclopentanol-forming cyclizations mediated by SmI2 results in excellent diastereocontrol. The C-Si bond in the products of cyclization provides a versatile handle for further manipulation. An asymmetric route to cyclization substrates involving copper-catalyzed silyl transfer has also been developed.
Addition conjuguee de derives lithies de dithianne-1,3 aux aldehydes αβ ethyleniques
作者:L. Wartski、M. El Bouz
DOI:10.1016/0040-4020(82)80108-7
日期:1982.1
In order to synthesize γ carbonyl aldehydes which are interesting precursors in organic synthesis, we examine the action of masked acylanions, the lithiated derivatives from 1,3 dithiane 1a and 2-phenyl-1,3- dithiane on selected unsaturated aldehydes: crotonaldehyde 2, cinnamaldehyde 3 3-methyl butenal 4 and methacrolein 5. In THF 1a leads with the four aldehydes to allylic alcohols. However 1b gives
Samarium(II)-mediated 4-exo trig ketyl-olefin cyclisation of unsaturated aldehydes. A general, stereoselective synthesis of functionalised cyclobutanols
作者:Derek Johnston、Catherine M. McCusker、David J. Procter
DOI:10.1016/s0040-4039(99)00910-7
日期:1999.6
gamma,delta-Unsaturated aldehydes having a quaternary centre in either the a or beta-position, have been prepared from substituted gamma-butyrolactones and undergo efficient 4-exo-trig ketyl-olefin cyclisation on treatment with samarium(II) iodide to give functionalised cyclobutanols. In all cases cyclisation occurs with complete diastereocontrol to give anti-cyclobutanol products. In the cyclisation of substrate 4ab, significant stereochemical control is achieved at three contiguous chiral centres. Both unsaturated esters and vinyl sulfones have been employed as substrates in the reaction. (C) 1999 Elsevier Science Ltd. All rights reserved.
WARTSKI, L.;EL, BOUZ, M., TETRAHEDRON, 1982, 38, N 22, 3285-3289
作者:WARTSKI, L.、EL, BOUZ, M.
DOI:——
日期:——
The Remarkable Effect of Cosolvent on a Samarium(II)-Mediated 4-<i>exo-trig</i> Cyclization: Further Synthetic Studies on Pestalotiopsin A
作者:David J. Edmonds、Kenneth W. Muir、David J. Procter
DOI:10.1021/jo026827o
日期:2003.4.1
A samarium(II)-mediated 4-exo-trig cyclization in which a remote stereocenter serves to control the facial selectivity of the cyclization is described. The apparent coordination of a tert-butyldimethylsilyl ether to the samarium center appears to give rise to the selectivity. The remarkable effect of the cosolvent, 2,2,2-trifluoroethanol, on the cyclization of this substrate, is also discussed. A stereoselective synthesis of the general class of gamma,delta-unsaturated aldehyde cyclization substrate is reported, and the utility of the cyclization is demonstrated in an approach to the fully functionalized core of pestalotiopsin A.