Competition between Novel 8- endo-dig and 6- trig Cyclizations of Samarium Ketyls Leading either to Benzannulated Cyclooctene or to Hexahydronaphthalene Derivatives
摘要:
Ketoesters 3a-3h with an alkynylaryl substituent were prepared by standard methods starting from siloxycyclopropanes 6a and 6b. Their reactions with 2.2 equiv. of samarium diiodide in the presence of hexamethyl phosphoramide either produced benzannulated cyclooctenol derivatives 4b (or lactone 9), 4f, 4g, and 4h or hexahydronaphthalene derivatives 5a, 5c, and 5d. The competition between 8-endo-dig and 6-trig cyclizations strongly depends on the substitution pattern of 3. Plausible explanations for this competition and of the diastereoselectivity observed are presented in this paper. (C) 2000 Elsevier Science Ltd. All rights reserved.
Samarium Diiodide in the Synthesis of Medium-Sized Rings - Carbocycles and Heterocycles by Intramolecular Addition of Samarium Ketyls to Alkynes
作者:Hans-Ulrich Reissig、Alexandra Hölemann
DOI:10.1055/s-2004-835657
日期:——
A series of alkynyl-substituted ketones and aldehydes was subjected to samariumdiiodide in the presence of HMPA to study the scope and limitations of their ketyl-alkyne coupling. Seven- and eight-membered heterocycles such as 4, 6, 8, 25, 27, 29, 33, and 35 could be isolated in moderate to good yields. Other cyclization products were isolated in low yields only. The efficacy of the reductive cyclization