Table 3. Optimization of conditions and substrates for the cyclization of guanidine and urea building blocks with 12.

Entry	Substrate	Base	Solvent	Temperature	Product	Yield
1	a13a	NaOMe	MeOH	65 °C	14a	32%
2	13b	K2CO3	Dioxane	100 °C	14b	11%
3	13c	K2CO3	Dioxane	100 °C	14a	b100%
4	13d	K2CO3	MeCN	100 °C	14d	72%
5	13e	K2CO3	Dioxane	100 °C	14e	17%
6	13e	K2CO3	MeCN	100 °C	14e	22%

^a13a (2.4 equiv.), base (3.4 equiv.).

^bNo purification of product required.