Optimization of exocyclic amine 2 protection using N,N-dimethylformamide dimethyl acetal^a.

Entry	Temp (°C)	Time (h)	Solvent	Yielde (%)
1	RT	48	DMF	66
2	65	24	DMF	58
3b	65	24	DMF	57
4c	65	24	DMF	55
5d	65	1	DMF	59
6	65	24	DMA	52
7	65	24	Pyridine	57
8f	65	24	—	71

^aUnless otherwise stated, the reactions were performed on a 0.10 mmol scale using 2 (1.0 equiv.) and N,N-dimethylformamide dimethyl acetal (4.0 equiv.) in the corresponding solvent (1.0 mL organic solvent).

^bReaction performed with MS 4 Å (50 mg).

^cReaction performed with MgSO₄ (50 mg).

^dReaction was performed in a microwave synthesizer at 200 W, 17 PSI.

^eYield represents a mixture of diastereomers (for entries 1–7 the reaction resulted in 3a as the major diastereomer and 3b as the minor diastereomer).

^fReaction yielded 3b as the only diastereomer. DMF: N,N-dimethyl formamide; DMA: N,N-dimethyl formamide acetal. Reactions were performed in duplicate and yields shown are an average. Note: 3a and 3b are separable diastereomers; stereochemical assignments of the imines of 3a and 3b were not conducted since both protecting groups are ultimately cleaved.