Optimization of the Ti-catalyzed [2 + 2 + 1] heterocoupling of 1a-BBN with 2^a.

Entry	% [Ti]b	Solvent	[py] equiv.c	Yieldd (selectivitye)
1	5	PhCF3	0.2	7% (12.5 : 1)
2	5	C6D5Br	0.2	22% (6.2 : 1)
3	10	C6D5Br	0.4	74% (17.1 : 1)
4	15	C6D5Br	0.6	65% (13.2 : 1)
5	10	PhCH3	0.4	67% (19.6 : 1)
6	10	PhCF3	0.4	55% (15.7 : 1)
7	10	PhOCH3	0.4	20% (9.6 : 1)
8f	10	C6D5Br	0.4	66% (22.7 : 1)

^aConc. = 0.2 M.

^b[PhNNPh] was adjusted coordinatingly to the change in [Ti] to keep the nitrene equivalent as 1, on basis of the relationship [nitrene] = [Ti] + 2[PhNNPh].

^cTotal equivalent of pyridine in the reaction.

^dYield determined by GC-FID.

^eSelectivity with respective to all possible pyrrole products.

^f t = 0.5 h.