Substrate Directed Regioselective Monobromination of Aralkyl Ketones Using N-Bromosuccinimide Catalysed by Active Aluminium Oxide: α-Bromination versus Ring Bromination

Table 5

Exploring of suitable catalyst for nuclear bromination^a.

Entry	Catalyst	Temp/°C	Time/h	Product	Yield^b/%	Selectivity; 4a : 5a : 𝟏𝐩^c
1; 1	—; —	32	24	—	—; 0	—; —
2	—	65	24	—	—	—
3	Acidic Al2O3	32	2	4a	43	43 : 16 : 41
4	Acidic Al2O3	65	0.3	4a	58	58 : 22 : 20
5	Neutral Al2O3	32	1.5	4a	62	62 : 21 : 17
6	Neutral Al2O3	65	0.12	4a	86	86 : 12 : 02

aReaction conditions: 4′-hydroxy acetophenone 1p (10 mmol), N-bromosuccinimide (12 mmol), 10% (w/w) catalyst, and methanol (20 mL) at reflux temperature.
bIsolated yield.
cUnreacted 4′-hydroxy acetophenone (1p).