The first examples o f 1,7,1,4,7,8-dialkyltriazaborabicyclo[3.3.0]octane.s 1-3 [R = isopropyl ( I ) , R = 1phenylbenzyl (Z), R = 1-methylbenzyl (3)] are reported. The bulky substituents prevent dimerization and make the syntheses feasible. The structures and confornations of the new compounds were studied by NMR spectroscopy. A chiral bicycle 3 (R,R) was also prepared.
RESULTS AND DISCUSSION
A few examples of triazaborabicycles have been known for a long time, triazaboradecalin (4) and its derivatives being the most studied [3,4]. Triazaborahydrindane [5] (5) has also been reported as well as 1,6,10,1 l-triazaborabicyclo-[5.4.O]undecane [6] 6 (Figure 1).
To our knowledge, the bicycle formed with two five-membered rings has not been described in the literature. In compounds 4-6, the ring size allows a planar boron atom and a strong retrocoordination from nitrogen to boron that stabilizes these molecules [3-61. An attempt to obtain the parent compound (R = H) of 1-3 was unsuccessful [5]. An explanation of this fact could be that the presence of two five-membered rings causes the boron atom to lose its planar structure, the strong cyclic strain forcing the boron to be in a tetrahedral arrangement, thus losing the back donation from nitrogen and making it acidic and reactive. The phospha-"To whom correspondence should be addressed.