Synthesis of Phenols via Metal-Free Hydroxylation of Aryl Boronic Acids with Aqueous TBHP

Table 2

Optimization of hydroxylation parameters^a.

Entry	Oxidant (equiv.)	Base (equiv.)	Temp. (°C)	Time (h)	Yield (%)^b,c
1	TBHP (1)	Cs2CO3 (1)	70	3	47
2	TBHP (2)	Cs2CO3 (1)	70	5	50^d
3	TBHP (2)	K2CO3 (0.5)	60	5	25
4	TBHP (2)	K2CO3 (1)	25	5	10
5	TBHP (2)	Pyridine (1)	60	10	NR
6	TBHP (2)	Et3N (1)	60	5	NR
7	TBHP (2)	Et2NH (1)	60	5	22
8	TBHP (2)	NaOH (1)	50	5	76
9	TBHP (2)	NaOH (1)	25	5	45
10	TBHP (2)	NaOH (1)	80	2	60
11	—	NaOH (1)	50	5	NR
12	TBHP (2)	—	50	5	Traces
13	TBHP (2)	KOH (1)	50	5	80
14	TBHP (2)	KO^tBu (1)	50	5	92(87)^e

^aReaction conditions: phenylboronic acid (1 mmol), aqueous TBHP base, and water (1 mL) stirred at designated temperature and time; ^bIsolated yield after workup; ^cProducts were characterized by MP, FTIR, and ¹H- and ¹³C-NMR; ^dTHF was added to mix reactants. ^eYield after 2 hours.