Scope and Mechanism for Lewis Acid-Catalyzed Cycloadditions of Aldehydes and Donor−Acceptor Cyclopropanes: Evidence for a Stereospecific Intimate Ion Pair Pathway
作者:Patrick D. Pohlhaus、Shanina D. Sanders、Andrew T. Parsons、Wei Li、Jeffrey S. Johnson
DOI:10.1021/ja8015928
日期:2008.7.1
In this work, the one-step diastereoselective synthesis of cis-2,5-disubstituted tetrahydrofuransviaLewis acid catalyzed [3 + 2] cycloadditions of donor-acceptor (D-A) cyclopropanes and aldehydes is described. The scope and limitations with respect to both reaction partners are provided. A detailed examination of the mechanism has been performed, including stereochemical analysis and electronic profiling
Enantiospecific Sn(II)- and Sn(IV)-Catalyzed Cycloadditions of Aldehydes and Donor−Acceptor Cyclopropanes
作者:Patrick D. Pohlhaus、Jeffrey S. Johnson
DOI:10.1021/ja055777c
日期:2005.11.23
A cycloaddition strategy for the synthesis of highly enantioenriched 2,5-cis-disubstituted tetrahydrofurans has been developed. In the presence of catalytic Sn(OTf)2 or SnCl4, a range of aldehydes will undergo formal [3 + 2] cycloadditions with a scalemic donor-acceptor cyclopropane to form optically active heterocycles. Mechanistic studies support an unusual SN2 attack by the aldehyde on the activated
Highly Diastereoselective Synthesis of Tetrahydrofurans via Lewis Acid-Catalyzed Cyclopropane/Aldehyde Cycloadditions
作者:Patrick D. Pohlhaus、Jeffrey S. Johnson
DOI:10.1021/jo048230+
日期:2005.2.1
A one-step procedure for the preparation of 2,5-disubstituted tetrahydrofurans from donor-acceptor cyclopropanes and aldehydes has been developed. In the presence of a catalytic amount of Sn(OTf)(2), cyclopropanes bearing an aryl or conjugated donor substituent vicinal to a malonyl diester group undergo cycloadditions with diverse conjugated aldehydes furnishing tetrahydrofurans with high cis diastereoselectivity. This method is useful for the preparation of regiodefined tetrahydrofurans.