Table 2. Efforts to Optimize Amide Formation to Prepare Compound 31.

entry	coupling agent	additive	base	yield (%)a
1	COMU	none	i-Pr2NEt	17c–35b
2	COMU	none	TMP	11b
3	COMU	none	2,6-lutidlne	58b
4	HBTU	none	2,6-lutidlne	traceb
5	EDC	none	none	24b
6	EDCd	HOBt	none	29b–32c
7	DCC	none	none	traceb
8	DCC	N-hydroxyphthalimide	Et3N	26b–28c
9	DCC	HOBt	none	66b–74c

^aIsolated yield after chromatography.

^bSmall scale (≤0.1 mmol).

^cLarge scale (≥1 mmol).

^dCH₂Cl₂ was used.