Beiträge zur Chemie des Bors, 217. [2 + 2]1‐Cycloadditionsreaktionen von 9‐Fluorenyliden‐(tetramethylpiperidino)boran mit Carbonyl‐und Thiocarbonyl‐Verbindungen

Contributions to the Chemistry of Boron, 217 [1] . – [2 + 2] Cycloaddition Reactions of 9‐Fluorenylidene(tetramethylpiperidino)borane with Carbonyl and Thiocarbonyl Compounds Amino‐9‐fluorenylidene‐borane 1 reacts with acetone or benzophenone in a [2 + 2] cycloaddition manner to give stable 1,2‐oxaboretane derivatives 2 . Aldehydes behave similarly but the oxaboretanes formed decompose readily. The esters MeCO 2 Et and MeCC – CO 2 Me as well as Cp(CO) 2 Fe – COCH 3 also provide access to novel oxaboretane derivatives ( 2e, f, h ). In contrast, no oxaboretane is obtained from 1 and MeC(O)NMe 2 and only (tmpBO) n ( n 2, 3) was isolated as a decomposition product. The amides MeC(O)NHMe and MeC(O)NH 2 also provide no access to cycloaddition since their NH bonds insert into the BC double bond of 1 . Thioketones react with 1 to yield 1,2‐thiaboretanes 5 . Tetramethyl‐cyclobutan‐1‐one‐3‐thione 8 adds 1 at its carbonyl function regiospecifically to form 9 . No reaction between 1 and CO 2 was observed, but COS produces an 1,2‐oxaboretane‐4‐thione 7 , and CS 2 in the form of [CpFe(CO) 2 ] 2 CS 2 the corresponding 1,2‐thiaboretane‐4‐thione 10 . Analogously, the ketimine Ph 2 CNMe adds to 1 producing the 1,2‐azaboretidine 11 . X‐ray structure determination of the 1,2‐oxaboretane 2h reveals a butterfly structure (folding anlge: 159.9°) of the four‐membered ring in contrast to the 1,2‐thiaboretane 5a whose four‐membered ring is almost planar, the folding angle being 176.9°.