Synthese von C ‐substituierten 2,5‐Dihydro‐1 H ‐borolen (3‐Borolenen)

Synthesis of C ‐substituted 2,5‐Dihydro‐1 H ‐boroles (3‐Borolenes) Magnesium‐diene addition compounds derived from isoprene, 2,3‐dimethylbutadiene, and 1,2‐dimethylenecyclohexane are treated with boron halides BCl 2 (NR 2 ) (R = Me, Et, i Pr), PhBCl 2 , or MeBBr 2 to give C ‐substituted 2,5‐dihydro‐1 H ‐boroles (3‐borolenes) 3–5. In a new in situ procedure 1,3‐pentadiene reacts with Mg/BCl 2 (NR 2 ) in THF to yield 2‐methyl derivatives 2‐MeC 4 H 5 BNR 2 ( 2 ). The NMe 3 adduct of 4,5,6,7‐tetrahydro‐2‐methyl‐2‐boraindan 5e · NMe 3 undergoes a topomerization with Δ G 290 = 59· 2 kJ/mol in a dissociative‐associative process. The crystal structure of 3,4‐dimethyl‐1‐phenyl‐3‐borolene ( 4d ) has been determined. The molecule displays a classical planar structure. There are no indications for specific intermolecular interactions.