Examination of potential heteroatom-substituted alkyne partners in Ti-catalyzed [2 + 2 + 1] heterocoupling^a.

Entry	X	Product	Yield	Selectivityb
1d			19%	2.5 : 1 (1.1 : 1)c
2e			7%	22.3 : 1 (12.5 : 1)
3e			51%	6.4 : 1 (4.5 : 1)
4d			7%	n.d.f

^aConc. = 0.2 M.

^bSelectivity with respect to all heterocoupling pyrrole regioisomer products. Selectivity = 3a-M/(4a-M + 5a-M). In parenthesis: selectivity with respect to all possible pyrrole products. Selectivity in parenthesis = 3a-M/(4a-M + 5a-M + homocoupled products of 2).

^cSelectivities calculated for major heterocoupling product 5a-M instead of 3a-M.

^d t = 16 h.

^e t = 20 h.

^fOther pyrrole products cannot be quantified due to their low yield and peak overlapping.