Catalytic β-Bromohydroxylation of Natural Terpenes: Useful Intermediates for the Synthesis of Terpenic Epoxides

Table 6

Bromohydroxylation and epoxidation of natural terpenes.

Entry	Terpenes 1b–1f		Bromoalcohols 2b–2f	Isolated yield 2b–2f (%)	Epoxides 3b–3d	Isolated yield 3b–3d (%)
1	1b	R1: CH3		93		70
		R2: CH3
		R3: 5-hydroxy-3-methylpentyl
2	1c	R1; CH3		78		60
		R2: CH3
		R3: 5-hydroxy-3-methylpent-3-enyl
3	1d	R1: CH3		80		60
		R2: 4-methyl-5-oxocyclohex-3-enyl
		R3: H
4	1e	R1: CH3		64		65
		R2: CH3
		R3: 3-methyl-5-oxopentyl
5	1f	R1: CH3		50	—
		R2: CH3
		R3: 3-methyl-5-oxopent-3-enyl

Reaction conditions: terpene 0.4 g, NBS 1.3 equiv.; diethylamine 2 equiv., catalyst (Dowex Marathon A, Cl⁻ form) 0.04 g, 5 mL acetone/H₂O 4 : 1 (v/v), r.t.