PREPARATION OF 8-MEMBERED CYCLIC ETHERS BY LEWIS ACID PROMOTED ACETAL ALKENE CYCLIZATIONS

被引：86

作者：

BLUMENKOPF, TA ^{[1
]}

BRATZ, M ^{[1
]}

CASTANEDA, A ^{[1
]}

LOOK, GC ^{[1
]}

OVERMAN, LE ^{[1
]}

RODRIGUEZ, D ^{[1
]}

THOMPSON, AS ^{[1
]}

机构：

[1] UNIV CALIF IRVINE,DEPT CHEM,IRVINE,CA 92717

来源：

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY | 1990年 / 112卷 / 11期

关键词：

D O I：

10.1021/ja00167a041

中图分类号：

O6 [化学];

学科分类号：

0703 ;

摘要：

The Lewis acid promoted cyclization of 20 5-alkenyl acetals is reported. Oxocenes with Δ4 unsaturation (3,6,7,8-tetrahydro-2H-oxocins) can be accessed in this convenient fashion with moderate to excellent efficiency and with perfect regiochemical fidelity. The yield of Δ4-oxocene increases as the 5-substituent of a 5-hexenyl acetal is varied from H to SiMe3 to SPh. High yields (up to 80%) are obtained in vinyl sulfide-acetal cyclizations only. Cyclizations of vinylsilane or vinyl sulfide acetals derived from secondary alcohols proceed with excellent (>25:1) stereoselectivity to construct, in a single step, cis-2,8-disubstituted-Δ4-oxocenes. The competing pathway that is most significant in undermining the yield of Δ4-oxocene in cyclizations of 5-(trimethylsilyl)-5-hexenyl acetals is not bimolecular oligomerization reactions, but rather cyclization to form 2-oxocanyl cations. The importance of this latter pathway was established by the isolation of oxocanyl acetals (47, 48, and 50), alkylated oxocanes (15 and 16), and 11-oxabicyclo[5.3.1]undecanes (20 and 54). These studies establish that carbon-carbon bond-forming cyclizations that form eight-membered-ring ethers can be high yielding even with simple substrates that lack conformational bias. © 1990, American Chemical Society. All rights reserved.

引用

页码：4386 / 4399

页数：14

共 78 条

[1]

ALLENBACH JH, 1988, NACHR CHEM TECH LAB, V36, P179

[2] CONFORMATION OF 8-MEMBERED OXYGEN HETEROCYCLES (OXOCANES) - EVIDENCE FROM 251-MHZ H-1 NUCLEAR MAGNETIC-RESONANCE [J].