Synthesis of Fused Bicyclic Systems with Nitrogen Atom at the Bridgehead, Including Indolizidines and Quinolizidines
作者:Antonella Pepe、Michael Pamment、Gunda I. Georg、Sanjay V. Malhotra
DOI:10.1021/jo102558u
日期:2011.5.6
Monocyclic as well as fused bicyclic systems with a nitrogen 10 atom at the bridgehead, including indolizidines and quinolizidines, can be prepared in four steps from N-Boc β-lactams. These easily prepared, highly robust, and flexible building blocks allow the incorporation of chirality and structural diversity, rendering the method feasible for diversity- as well as target-oriented synthesis.
N -Boc β-内酰胺可以通过四步制备单环和稠合双环系统,在桥头处有一个 10 原子的氮原子,包括吲哚里西啶和喹尼西啶。这些易于制备、高度稳健且灵活的构建模块允许结合手性和结构多样性,使该方法适用于多样性以及面向目标的合成。
Photocatalytic Intramolecular Alkene Hydroamination of <i>N</i>-Alkoxy Ureas: An Approach to Imidazolinones
in good yields by intramolecular hydroamination of N-alkoxy ureas in the presence of an organic photocatalyst and an inorganic base. In this reaction, the N-alkoxy urea anion generated by deprotonation undergoes photocatalyzed single-electron-transfer oxidation to generate the correspondingradical, which cyclizes to afford the imidazolinone ring. This new protocol grants access to an array of complex
Regiochemical and stereochemical studies on halocyclization reactions of unsaturated sulfides
作者:Xiao-Feng Ren、Edward Turos、Charles H. Lake、Melvyn Rowen Churchill
DOI:10.1021/jo00125a038
日期:1995.10
The regiochemistry and stereochemistry for the halocyclization reactions of unsaturated benzyl sulfides have been examined as a function of tether length, type of unsaturation (carbon-carbon double bond versus carbon-carbon triple bond), substituents, and halogenating agent. Alkenyl sulfides were found to react with iodine or bromine at room temperature to give five-membered ring cycloadducts exclusively over those having four-membered rings, while for larger systems, six-membered ring products are formed preferentially over their five-membered ring isomers and exclusively over the seven-membered ring adducts. The endo- versus exo-regioselectivity of these alkenyl sulfide ring closures most likely reflects the difference in thermodynamic stabilities of the beta-halo sulfide cycloadducts, which are able to equilibrate via a common episulfonium intermediate. The efficiency of the cyclization process markedly drops off for these alkenyl sulfides as the tether length increases beyond four intervening carbon centers. Thus, while the halogenations of 3-butenyl sulfides and 4-pentenyl sulfides give high yields of cycloadducts, those of 5-hexenyl sulfides afford only small amounts of cyclized products and large quantities of acyclic dibromides. Conversely the reactions of acetylenic sulfides with iodine give uniformly high yields and regiochemical control regardless of the tether length. Thus, 3-butynyl and 4-pentynyl sulfides cyclize cleanly to the five-membered ring while 5-hexynyl sulfides give exclusively the six-membered ring, The products arising from these alkynyl sulfide ring closures are believed to be formed under kinetic control. The methodology has been applied to the synthesis of unusual bicyclic beta-lactams related to the penicillin family of antibiotics.
Biocatalysis of precursors to new-generation SB-T-taxanes effective against paclitaxel-resistant cancer cells