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

Table 1

Exploring of catalyst and other reaction conditions for α-bromination of 1a using NBS^a.

Entry	Catalyst	Temp/°C	Time/h	Product	Yield^b/%	Selectivity/%; 2a : 3a : 𝟏𝐚^c
1; 1	—; —	32	24	—	—; 0	—; —
2		65	24	—	—	—
3	Acidic Al2O3	32	1.3	2a	61	61 : 18 : 21
4	Acidic Al2O3	65	0.1	2a	89	89 : 08 : 03
5	Neutral Al2O3	32	2.0	2a	48	48 : 19 : 33
6	Neutral Al2O3	65	0.12	2a	66	66 : 12 : 22

aReaction conditions: acetophenone 1a (10 mmol), N-bromosuccinimide (12 mmol), 10% (w/w) catalyst, and methanol (20 vol) at reflux temperature.
bIsolated yield of product 2a.
cUnreacted acetophenone.