US EPA

7616296 

Journal Article 

On the reactivity of germaethene Me(2)Ge=C(SiMe(3))(2): Mechanistic aspects of Diels Alder and ene reactions 

Wiberg, N; Wagner, S; , 

1996 

1 

Zeitschrift für Naturforschung B
ISSN: 0932-0776 

VERLAG Z NATURFORSCH 

TUBINGEN 

838-850 

WOS:A1996UV83600014 

Diels-Alder and ene reactions of germaethene Me2Ge=C(Sime3)2 (2) with butadienesGRAPHICSand propenesGRAPHICSrespectively, take place regioselectively, as well as stereoselectively. They are accelerated by an increasing tendency of substituents in butadiene or propene to donate electrons (e.g. 2-methylbutadiene > butadiene; 2-methylpropene > propene), and retarded by an increasing bulkyness of substituents in 1,4- or 1,3-positions (e.g. 1-methylbutadiene > 2-methylbutadiene; 1-vinylpropene > propene). It is concluded from these studies that Diels-Alder and ene reactions of 2 occur - like those of Me(2)Si=C(SiMe(3))(2) (1) or of ethenes > C=C < - in a concerted way and are HOM(diene)-LUMO(dienophile) and HOMO(ene)-LUMO(enophile) controlled. Thus 2 and 1 behave as carbon analogues. With regard to a specific diene or ene (e.g. anthracene; toluene), 2 is better dienophile or enophile than 1 or ethenes. With a fixed diene/ene mixture (e.g. butadiene/propene). 2 acts as the better dienophile, while 1 is better enophile. These results can be explained by the pi/pi*-energy difference and the double bond polarity decreasing in the direction 1>2. Only cis-piperylene gives a [2+2] cycloadduct with 2. besides two [4+2] cycloadducts, and an ene reaction product.