Beiträge zur Chemie des Bors, 190 [1] Synthese und Molekülstruktur von 1,2-Dihydroboreten und Azadiboretidinen / Contribution to the Chemistry of Boron, 190 [1] Synthesis and Molecular Structure of 1,2-Dihydrodiboretes and Azadiboretidines

[2+2]-Cycloadditions of 9-Fluorenylidentetramethylpiperidinoboranes have been studied with selected olefines, acetylenes and iminoboranes. No reactions with olefines were observed. While propiolic methylester reacts exclusively at the carbonyl bond producing the oxaboretane 5, alkines such as diethylamino-alkines, cyclo-octine and phenylacetylene provide access to the'1,2-dihydroboretenes 6, 3 and 2. Tetramethylpiperidinoiminoboranes make 1.2.4-azadiboretidines 7 available. 6a and 7a contain a folded four-membered ring as shown by X-ray structure analysis. There is only a weak 1,3-intraannular interaction due to BN-;r-bonding of the boron atoms with their exocyclic amino group.