From bis(silylamino)tin dichlorides via di(1-alkynyl)-bis(silylamino)tin to new heterocycles by 1,1-organoboration

Bis(silylamino)tin dichlorides 1 [X2SnCl2 with X=N(Me3Si)2 (a), N(9-BBN)SiMe3 (b), N(tBu)SiMe3 (c), and N(SiMe2CH2)2 (d)] were prepared from the reaction of two equivalents of the respective lithium amides (Li-a–d) with tin tetrachloride, SnCl4, or from the 1:1 reaction of the respective bis(amino)stannylene with SnCl4. The compounds 1 react with two equivalents of lithium alkynides LiCCR1 to give the di(1-alkynyl)-bis(silylamino)tin compounds X2Sn(CCR1)2, 2 (R1=Me), 3 (R1=tBu), and 4 (R1=SiMe3). Problems were encountered, mainly with LiCCtBu as well as with 1b, since side reactions also led to the formation of 1-alkynyl-bis(silylamino)tin chlorides 5–7 and tri(1-alkynyl)(silylamino)tin compounds 8 and 9. 1,1-Ethylboration of compounds 2–4 led to stannoles 10, 11, and in the case of propynides, also to 1,4-stannabora-2,5-cyclohexadiene derivatives 12. The molecular structure of the stannole 11b (R1=SiMe3) was determined by X-ray analysis. The reaction of 2a and d with triallylborane afforded novel heterocycles, the 1,3-stannabora-2-ethylidene-4-cyclopentenes 14. These reactions proceed via intermolecular 1,1-allylboration, followed by an intramolecular 1,2-allylboration to give 14, and a second intramolecular 1,2-allylboration leads to the bicyclic compounds 15.