Stereochemical Outcomes in Reductive Cyclizations To Form Spirocyclic Heterocycles
作者:Matthew A. Perry、Richard R. Hill、Justin J. Leong、Scott D. Rychnovsky
DOI:10.1021/acs.orglett.5b01422
日期:2015.7.2
Reductive lithiation and cyclization of N-Boc α-amino nitriles are often highly stereoselective. The alkyllithium intermediates are formed with varying levels of selectivity, but the alkyllithium geometry does not play a major role in the overall stereoselectivity. The final configuration is determined in the cyclization reaction, where both retention and inversion pathways are observed. Where strong
N -Bocα-氨基腈的还原锂化和环化通常具有很高的立体选择性。形成的烷基锂中间体具有不同的选择性水平,但烷基锂的几何形状在总体立体选择性中不发挥主要作用。最终构型是在环化反应中确定的,在该反应中观察到了保留和转化途径。在产物中存在强烈的热力学偏好的地方,动力学控制的烷基锂环化有利于更稳定的产物。
Proline-like β-turn mimics accessed via Ugi reaction involving monoprotected hydrazines
A four-center, three-component Ugi-type reaction of a variety of keto acids, Boc- or Cbz-protected hydrazine, and isocyanides offers a simple and high yielding access to cyclic products containing an N-aminolactam unit. The latter are shown to form consistently an intramolecular hydrogen bond leading to a p-turn-like secondary structure. The possibility of integrating such N-aminolactam units (without disruption of the folded structure) into pseudotripeptide fragments is demonstrated. (C) 2010 Elsevier Ltd. All rights reserved.
Sequenced Reactions with Samarium(II) Iodide. Sequential Intermolecular Carbonyl Addition/Intramolecular Nucleophilic Acyl Substitution for the Preparation of Seven-, Eight-, and Nine-Membered Carbocycles
作者:Gary A. Molander、Cristina Alonso-Alija
DOI:10.1021/jo980119e
日期:1998.6.1
Samarium(II) iodide has been employed to promote a tandem intermolecular carbonyl addition/intramolecular nucleophilic acyl substitution sequence, generating seven- through nine-membered monocyclic, bicyclic, and tricyclic ring systems with good yields and high diastereoselectivities. This tandem reaction consists of an intermolecular reaction followed by an intramolecular ring expansion that results in a formal [m + n] cycloaddition, starting from extremely simple, readily available substrates. The regioselectivity and stereoselectivity of the process arise from a tuning of the reducing power of samarium(II) iodide with nickel(II) iodide in the first step and irradiation with visible light in the second. By using this method, a variety of structural motifs have been assembled rapidly in good yields.