Silaheterocyclen, XXII. Diels‐Alder‐Reaktionen von Dichlor(neopentyl)silaethen mit Furanen und Umlagerung der erhaltenen Bicyclen zu monocyclischen Si – O‐Siebenring‐Verbindungen

Sila Heterocycles, XXII [1] . – Diels‐Alder Reactions of Dichloro(neopentyl)silaethene with Furans and Rearrangement of the Resulting Bicycles into Monocyclic Si – O Seven‐Membered Ring compounds The reaction of trichloro(vinyl)silane ( 1 ) and Li t Bu ( 2 ) initially leads to the α1‐lithio adduct Cl 3 SiCH(Li)CH 2 t Bu ( 3 ) which can be trapped by trimethylsilyl triflate yielding the C 1‐silylated product [Cl 3 SiCH(SiMe 3 )CH 2 t Bu ( 5 )]. 1,2‐LiCl elimination from 3 gives dichloro(neopentyl)silaethene [Cl 2 SiCHCH 2 t Bu ( 4 )] as intermediate. This can be established by insertion of 4 into the Si – O bond of Me 3 SiOMe to Cl 2 Si(OMe)CH(SiMe 3 )CH 2 t Bu ( 6 ). 4 is a dienophile of high activity and reacts with the furans 7 – 9 to give the [4 + 2] cycloaddition compounds 10 – 12 . These Diels‐Alder products are thermally unstable and decompose slowly at room temperature into the starting furans and tetrachlorodisilacyclobutane ( 15 ). Under thermolysis conditions (3 d/17°C) they rearrange into the monocyclic Si – O seven‐membered ring compounds 16 – 18 . A mechanism for the 7‐Oxa‐2‐silabicyclo[2.2.1]hex‐5‐en → 1‐Oxa‐2‐silacyclohepta‐4,6‐diene rearrangement is proposed.