Photoreductive cyclization of unsaturated aldehydes : An easy access to spiranic molecules
作者:J. Cossy、J.P. Pete、C. Portella
DOI:10.1016/s0040-4039(00)70697-6
日期:1989.1
The photoreductive cyclization of ω-unsaturated aldehydes is an efficient process which leads to substituted cycloalkanols. This process is used as a convenient approach to spiranic molecules.
ω-不饱和醛的光还原环化是导致取代的环烷醇的有效方法。此过程用作螺环分子的便捷方法。
Neighboring group participation in Lewis acid-promoted [3 + 4] and [3 + 5] annulations. The stereocontrolled synthesis of tricyclic ethers
作者:Gary A. Molander、Kimberly O. Cameron
DOI:10.1021/jo00074a018
日期:1993.10
A variety of 1,4- and 1,5-keto aldehydes derived from cycloalkanes are coupled with the bis(trimethylsilyl) enol ether of methyl acetoacetate in the presence of either TMSOTf or TrSbCl6 to generate tricyclic ethers. The reactions proceed with excellent regiochemical control by a mechanism involving neighboring group participation. This mechanism involves initial formation of a bicyclic oxocarbenium ion intermediate from the keto aldehyde substrates. The geometries of selected bicyclic intermediates have been optimized using the AM1 method allowing successful prediction of the stereochemical outcomes in the cyclization in most cases. Epimerization of alpha-chiral keto aldehyde substrates does not appear to occur in these Lewis acid-promoted annulation reactions.
Selective mono- and polymethylene homologations of copper reagents using (iodomethyl)zinc iodide
作者:AchyuthaRao Sidduri、Michael J. Rozema、Paul Knochel
DOI:10.1021/jo00062a010
日期:1993.5
A wide range of unsaturated aryl-, alkenyl-, alkynylcopper compounds can be selectively homologated by a methylene unit using (iodomethyl)zinc iodide or bis(iodomethyl)zinc. These reactions allow the generation of mixed allylic zinc-copper compounds which can be efficiently trapped with carbonyl compounds. An application to a general preparation of functionalized alpha-methylene-gamma-butyrolactones is described. The homologation of alkynylcoppers with (iodomethyl)zinc iodide allows a one-pot preparation of propargylic copper reagents which in the presence of a carbonyl compound provide various homopropargylic alcohols in excellent yields. In the absence of an electrophile, a clean quadruple methylene homologation of alkynylcoppers occurs to furnish dienic copper reagents. The homologation of other types of copper reagents is also possible, and carbanions at the alpha-position to amines as well as homoenolates of aldehydes or ketones can also be prepared by this method.