Highly Selective Diels-Alder Reactions of Directly Connected Enyne Dienophiles
作者:Mingji Dai、David Sarlah、Maolin Yu、Samuel J. Danishefsky、Gavin O. Jones、K. N. Houk
DOI:10.1021/ja065762u
日期:2007.1.1
The paper describes the course of cycloadditions of Diels-Alder dienophiles containing linked enyne sites, each substituted with activating groups. Consistently, it was found that in the enyne cases the Diels-Alder reaction occurred specifically at the acetylenic center. Furthermore, it was found that the regiochemical sense of the cycloaddition was apparently determined by the remote activating group bound to the olefinic site. This remote acrylyl group totally dominated the course of the cycloaddition, relative to the activating group bound directly on the acetylene site. Explanations for these findings at the computational level are provided. The computations also rationalize the strong preference for cycloaddition to occur at the acetylene linkage and encompass the otherwise surprising regiochemical dominance by the remote ester on the olefinic site. The high selectivities available through such reactions provide important new opportunities in the synthesis of orsenillate type substructures that are found in a variety of natural products of contemporary interest.
A Total Synthesis of Xestodecalactone A and Proof of Its Absolute Stereochemistry: Interesting Observations on Dienophilic Control with 1,3-Disubstituted Nonequivalent Allenes
作者:Toshiharu Yoshino、Fay Ng、Samuel J. Danishefsky
DOI:10.1021/ja064270e
日期:2006.11.1
A concise total synthesis of xestodecalactone A, utilizing a Diels-Alder strategy is described. The focal Diels-Alder reaction relied on an "ynoate" dienophile to rapidly assemble the required resorcylinic acid scaffold. During this study, Diels-Aldercycloaddition reactions involving 1,3-disubstituted nonequivalent allene dienophiles were studied, and some surprising results were encountered.