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 LitBu (2) initially leads to the α1‐lithio adduct Cl3SiCH(Li)CH2tBu (3) which can be trapped by trimethylsilyl triflate yielding the C1‐silylated product [Cl3SiCH(SiMe3)CH2tBu (5)]. 1,2‐LiCl elimination from 3 gives dichloro(neopentyl)silaethene [Cl2SiCHCH2tBu (4)] as intermediate. This can be established by insertion of 4 into the Si – O bond of Me3SiOMe to Cl2Si(OMe)CH(SiMe3)CH2tBu (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.