Diels-Alder and ene reactions of the stannaethene Me2Sn=C(SiMe3)(2): Dienophilic and enophilic behaviour of ethenes Me2E=C(SiMe3)(2) (E = Si, Ge, Sn)

Diels-Alder and ene reactions of stannaethene Me2Sn=C(SiMe3)(2) (3) with bu tadienes (C=C-C=C) and propenes (C=C-CH) take place both regioselectively a nd stereoselectively, These are accelerated by an increasing tendency of su bstituents in butadiene or propene to donate electrons (e.g. 2-methylbutadi ene > butadiene; 2-methylpropene>propene), and retarded by an increasing bu lkiness of substituents in 1,4- or 1,3-positions (e.g. 1-methylbutadiene < 2-methylbutadiene; 1-vinylpropene <propene). It is concluded that Diels - A lder and ene reactions of 3 occur-like those of the germaethene Me2Ge=C(SiM e3)(2) (2), the silaethene Me2Si=C(SiMe3)(2) (1) or the ethenes-in a concer ted way and are HOMOdiene-LUMOdienophile and HOMOene - LUMOenophile control led, Thus 3 as well as 2 and 1 behave as carbon analogues, With regard to a specific diene or ene (e.g, anthracene; toluene), 3 like 2 is a better die nophile or enophile than 1 or ethenes, With a fixed diene/ene mixture (e.g. butadiene/propene), the enophilicity of Me2E=C(SiMe3)(2) increases at the cost of the dienophilicity in direction ethenes much less than germaethene 2<stannaethene 3<silaethene 1. These results can be explained by the pi/pi* energy differences, the double-bond polarities and the E-C bond energies.