New Regio- and Stereocontrolles Reactions of 2-Vinylindoles with CC-Dienophiles: Diels-Alder Reactions, Ene Reactions and Michael Additions

The reactions of selectively functionalieed 2-vinylindoles with some acyclic and cyclic CC-dienophiles yield Diels-Alder adducts, Diels-Alder ene products, and Michael adducts, respectively, with very high regio-and/or stereoselectivities.This methodology provides a convenient access to functionalized indoles, carbaeoles, and [c]pyrroloannellated carbaeoles with substitution patterns that are not so easily accessible by other routes.Diels-Alder reactions of vinylindoles have been found by and by ~s ~, ~-~t o represent a synthetically very attractive concept for the preparation of novel [blannellated indoles to serve as lead substances and as building blocks for alkaloids.However, the synthetic potential and limitations of the concept, as well as the analytical methodology required by the alternative reaction pathways, especially when 2-vinylindales are used, have not yet been sufficiently delineated to allow use of the concept in the planning of syntheses of condensed heterocy-~l e s 4 -~.Thus, in continuation of our synthetic investigations on vinylheterocycles, we now report on some new and interesting reactions of selected, principally donor-and acceptor-substituted, 2-vinylindoles 1 with acyclic and cyclic CCdienophiles and, at the same time, illustrate the competing reaction pattern of "Diels-Alder reaotion, Diels-Alder ene reaction, and Michael a d d i t i ~n " ~' ~.This pattern is markedly less frequently found in such a state of completeness in the 3-vinylindole series4.In the present communication on the reactions of la-i with methyl propynoate, methyl acrylate, 1-phenylmaleimide, 1-penten-?-one,and p-beneoquinone, only those combinations of reactants are discussed which, in our studies, produced a clear and structural-analytically perceivable reaction result.