Verhalten von cis ;‐2‐Boryl‐1‐stannylalkenen gegenüber (Dimethylamino)trimethylstannan, Methoxytrimethylstannan und Methanol – Aufbau neuer Zinn – Element‐Bindungen, Beispiele für Lösungsmittel‐gesteuerte Reaktionen

Behaviour of cis ;‐2‐Boryl‐1‐stannylalkenes Against (Dimethylamino)trimethylstannane, Methoxytrimethylstannane, and Methanol – Formation of New Tin – Element Bonds, Examples of Solvent‐Controlled Reactions When alkene derivatives 1 [Me 3 Sn(R 1 )CC(R)BR 2 ], with the trimethylstannyl‐ and the dialkylboryl group in cis position at the CC double bond, are treated with (dimethylamino)‐trimethylstannane ( 4 ), methoxytrimethylstannane ( 5 ), or methanol, the product distribution depends remarkably on the solvent [hexane or tetrahydrofuran (THF)]. In hexane, 1a, b (R 1 =H, REt, Pr) react with 4 to give the B ‐dimethylamino compounds 6a, b in high yields as a result of addition and rearrangement. Other derivatives 1 do not react with 4 in hexane. Under the same conditions in hexane some alkenes 1 react with 5 to yield the B ‐methoxy derivatives 8 , which are analogous to 6 . A complex mixture of various products is obtained from the reaction of 1 with methanol in hexane. If the same reactions are carried out in THF, many compounds 1 react with 4 and 5 to eliminate tetramethyltin and give dihydro‐ 1,2,5‐azonia‐ ( 7 ) or dihydro‐1,2,5‐oxoniastannaboratoles ( 9 ), respectively. The reaction with methanol in THF also leads to the oxonia‐stannaboratoles 9 , this time by elimination of methane. Pure samples of compound 9g are obtained as the crystalline THF adduct 9g ‐THF. A mechanism is proposed involving adduct formation at the boryl group, followed by intramolecular reactions depending on the donor quality of the respective solvent.