Definition of Several Control Elements Relevant to the Stereodefined Serial Elaboration of Belted Poly(spirotetrahydrofurans) Fitted with a Cyclohexane Core
摘要:
The stereochemistry of the condensations of 2-cyclohexenones, alpha-arylidenecyclohexanones, and alpha-(tert-butyldimethylsiloxy)cyclohexanones carrying one or two (both syn and anti) spirotetra-hydrofuran units adjacent to the carbonyl with allyl organometallics (especially indium) and with the Normant reagent (ClMgO(CH2)(3)MgCl) is described. Good levels of anti stereoselection are observed in the alpha-arylidene series. Subsequent cyclization generates a second (or third) tetrahydrofuran ring possessing trans vicinal oxygens. Useful levels of matched and mismatched diastereoselection are also attainable by prior alpha-oxygenation, The intrinsic differences in diastereomer production between indium and magnesium organometallics are highlighted. A clear distinction regarding the anticipated direction of stereoselectivity is made on the grounds of chelation capabilities and the intra- or intermolecularity of carbon-carbon bond formation. Finally, the two protocols that are described in detail are shown to be iterative, a feature that augurs well for ultimately accessing the eight possible hexaspirocyclohexanes in an efficient and stereocontrolled manner.
Oxacycle Synthesis via Intramolecular Reaction of Carbanions and Peroxides
作者:Rachel Willand-Charnley、Benjamin W. Puffer、Patrick H. Dussault
DOI:10.1021/ja5026276
日期:2014.4.23
The intramolecular reaction of dialkyl peroxides with carbanions, generated via chemoselective metal-heteroatom exchange or deprotonation, provides a newapproach to cyclicethers. Applied in tandem with C–C bond formation, the strategy enables a one-step annelation to form oxaospirocycles.
π-Facial Diastereoselection in the 1,2-Addition of Allylmetal Reagents to 2-Methoxycyclohexanone and Tetrahydrofuranspiro-(2-cyclohexanone)
作者:Leo A. Paquette、Paul C. Lobben
DOI:10.1021/ja9536835
日期:1996.1.1
stereochemical course of the 1,2-addition of several allylmetal reagents and of the Normant Grignard [ClMgO(CH2)3MgCl] to 2-methoxycyclohexanone and tetrahydrofuranspiro-(2-cyclohexanone) has been determined. In four of the six substrates examined, a 4-tert-butyl group is present to serve as a conformational anchor. The neighboring methoxyl substituent is shown to be capable of engaging effectively in
Spiroketals via oxidative rearrangement of enol ethers
作者:David L. Waller、Corey R. J. Stephenson、Peter Wipf
DOI:10.1039/b612992g
日期:——
Oxidative rearrangement of cyclic enolethers leads to alpha-alkoxyesters. In the presence of a neighboring spiroether, this approach provides a stereoselective access to spiroketals. A modified proposal for the biosynthesis of acutumine is presented.
Radical cyclizations of diosphenol ω-haloalkyl ethers to oxabicycloalkanones
作者:Anthony A. Ponaras、Ömer Zaim
DOI:10.1016/s0040-4039(00)60470-7
日期:1993.4
Radical cyclization of diosphenol omega-haloalkyl ethers gives spiro- and fused oxabicycloalkanones.
Alkoxy radical accelerated β-fragmentation of alcohols and lactols
作者:James H Rigby、Anne Payen、Namal Warshakoon
DOI:10.1016/s0040-4039(01)00121-6
日期:2001.3
Treatment of alcohols and lactols with Pb(OAc)(4)/Cu(OAc)(2) in refluxing benzene provides the corresponding delta -unsaturated carbonyl products. (C) 2001 Elsevier Science Ltd. All rights reserved.