Formation of medium-size bridged ring systems via ring-closing metathesis of 2,5-disubstituted-2,3-dihydro-1H-pyrroles
作者:Samantha J. Bamford、Kees Goubitz、Hester L. van Lingen、Tim Luker、Henk Schenk、Henk Hiemstra
DOI:10.1039/a908272g
日期:——
A series of 2,5-disubstituted-2,3-dihydro-1H-pyrroles were prepared via diastereoselective alkylations of sulfone 10. Ring-closing metathesis (RCM), using Grubbs’ catalyst, provided bridged ring systems with newly formed 9- to 12-membered rings in moderate to good yields. The 9-membered ring was formed as a single Z-isomer whereas the 10- to 12-membered rings were formed as mixtures of E- and Z-isomers. It was shown that the minor diastereomer obtained from the alkylation product 11c failed to undergo RCM, illustrating the crucial aspect of substrate conformation.
Synthesis of Octahydro 1H-Pyrrolo[1,2-a]indol-3-ones Via Intramolecular Diels-Alder Reaction of 5-Substituted N-Dienyl Lactams
作者:Katherine Grant-Young、Michael B. Smith、Timo Ovaska、Chung-Jen Wang
DOI:10.1080/00397919809458704
日期:1998.11
Abstract N-dienyl-5-alkenyl-lactams can be prepared from succinimide. Heating leads to an intramolecular Diels-Alder cyclization that produces tricyclic products useful for the preparation of related alkaloids.
Tandem Radical Decarboxylation−Oxidation of Amino Acids: A Mild and Efficient Method for the Generation of <i>N</i>-Acyliminium Ions and Their Nucleophilic Trapping
作者:Alicia Boto、Rosendo Hernández、Ernesto Suárez
DOI:10.1021/jo000356t
日期:2000.8.1
derivatives have been prepared in order to test the scope and diastereoselectivity of this method. These substrates were treated with iodosylbenzene or (diacetoxyiodo)benzene (DIB) and iodine in order to generate the corresponding carboxyl radical, which evolves by loss of carbon dioxide to produce a carbon radical which in turn undergoes oxidation to an N-acyliminium ion. This postulated intermediate
Solid-state photodimerization of 2-phenylethenyl enamides
作者:Fengbin Song、Julie H. Snook、Bruce M. Foxman、Barry B. Snider
DOI:10.1016/s0040-4020(98)00806-0
日期:1998.10
Enamides 3a-c and 6 crystallize in α-packing modes with short intermolecular distances of 3.7–4.0 Å between alkene carbon atoms of adjacent molecules related by a center of symmetry. Irradiation at 350 nm of these crystalline tertiary phenylethenyl enamides affords head-to-tail dimers 8a-c and 9, respectively, in 87–92% yield, in marked contrast to the E to Z isomerization that is the exclusive reaction
of the pyrrolidine ring, and then the N,O-acetal is further oxidized by the o-benzoquinone to the γ-lactam. Because the first oxidation occurs selectively at the α-C–H of the pyrrolidine ring, oxidation-sensitive functional groups (allyl-, vinyl-, hydroxyl-, and amino groups) on pyrrolidine ring are unaffected. The synthetic utility of this novel method was demonstrated by the facile syntheses of (S)-vigabatrin