Optimization of the halo-Prins/halo-Nazarov coupling cascade for the formation of ketone-derived indolines^a.

Entry	Carbonyl partner 5a	Equiv.	Indoline 6a (yieldb)
1	Ketone	1.2	42%c
2		2.0	61%
3	Ketal	1.2	44%c
4		2.0	61%
5	Enol ether	1.2	49%c
6		2.0	81%

^aReaction conditions: 1e (0.1 mmol), 5a (equiv. in the table), TBAI (2.0 equiv.), TfOH (1.2 equiv.), DCM, −40 °C; then TfOH (0.2 equiv.), DCM/HFIP (10 : 1 v/v), 0 °C.

^bYield corresponds to the isolated yield of pure product 6a across two steps.

^cEnyne 1e was partially consumed.