Table 1.

Exploration of the metal-mediated oxidative cyclization of a tetrahydrobiladiene-ab^a

Entry	Metal salt	Baseb	Solvent	Product	Yield
1	Zn(OAc)2	TMPi	MeCN	ZnC-P10	37%c
2	Zn(OAc)2	DBU	MeCN	ZnC-P10	9%c
3	Zn(OAc)2	DIEA	MeCN	ZnC-P10	10%c
4	Pd(OAc)2	TMPi	MeCN	PdC-P10	12%d
5	Pd(OAc)2	KOHe	EtOH	PdC-P10	5.6%d
6	Pd(MeCN)2Cl2	KOHe	EtOH	PdC-P10	6.2%d
7	Cu(OAc)2	TMPi	MeCN	CuC-P10	4%c
8	Cu(OAc)2	KOHe	EtOH	CuC-P10	14%d
9	SnCl2	TMPi	MeCN	SnC-P10	5%
10	MgBr2	TMPi	MeCN	--	0%
11	Co(OAc)2	TMPi	MeCN	--	0%
12	NiCl2	TMPi	MeCN	--	0%
13	CdCl2	TMPi	MeCN	--	0%
14	No metal	TMPi	MeCN	--	0%
15	No metal	DBU	MeCN	--	0%
16	No metal	DIEA	MeCN	--	0%

^aThe crude biladiene 9b-Br was prepared by p-TsOH-catalyzed condensation of 5 and 8b under standard conditions. The reaction mixture was then neutralized by the base to be used in the metal-mediated oxidative cyclization (when KOH was used as a base in metal-mediated cyclization, crude 9b-Br was neutralized by triethylamine). Unless noted otherwise each reaction was performed at 10 mM concentration with 15 equiv of metal salt and 30 equiv of base.

^bBases include 2,2,6,6-tetramethylpiperidine (TMPi), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), and N,N-diisopropylethylamine (DIEA).

^cSpectroscopic yield (from 8b) unless noted otherwise, assuming a fixed molar absorption coefficient in all cases (see Experimental Section).

^dIsolated yield.

^e5 Equiv was employed.