Reactions of Boron-Derived Radicals with Nucleophiles.

Reactions of phenanthrenedione- and pyrenedione-derived borocyclic radicals, CHOB(CF) (n = 14 (1), 16 (3)), with a variety of nucleophiles have been studied. Reaction of 1 with P(t-Bu) affords the zwitterion 3-(t-Bu)PCHOB(CF) (5) in addition to the salt [HP(t-Bu)][CHOB(CF)] (6). In contrast, the reaction of 1 with PPh proceeds to give two regioisomeric zwitterions, 1-(PhP)CHOB(CF) (7a) and 3-(PhP)CHOB(CF) (7b), as well as the related boronic ester CHOB(CF) (2). In a similar fashion, 3 reacted with PPh to give 3-(PhP)CHOB(CF) (8a), 1-(PhP)CHOB(CF) (8b), and boronic ester CHOB(CF) (4). Reactions of secondary phosphines PhPH and tBuPH with 3 yield 3-(RPH)CHOB(CF) (R = Ph (9), t-Bu (10)). The reaction of 1 with N-heterocyclic carbene IMes afforded 3-(IMes)CHOB(CF) (11) and [IMesH][CHOB(CF)] (12), while the reactions with quinuclidine and DMAP afforded the species 3-(CHN)CHOB(CF) (13) and [H(NCH)][CHOB(CF)] (14), and the salt [9,10-(DMAP)CHOB(CF)][CHOB(CF)] (15), respectively. These products have been fully characterized, and the mechanism for the formation of these products is considered in the light of DFT calculations.