Table 1. Conditions a for the Sonogashira cross-coupling reaction of 5-bromoindole 15 and 5-bromotryptophan 18 with phenylacetylene 16 .
| Entry | Substrate | Cat/mol% | Ligand/mol% | Alkyne loading/eq. | Heating method | Reaction time/h | NMR conv./% |
| 1 | 15 | 2.5 | 7.5 | 1.5 | Conventional | 18 | 76 b |
| 2 | 15 | 5.0 | 15.0 | 1.5 | Conventional | 18 | 93 b |
| 3 | 15 | 5.0 | 15.0 | 3.0 | Conventional | 18 | >99 b |
| 4 | 15 | 5.0 | 15.0 | 3.0 | Microwave | 2 | >99 b |
| 5 | 18 | 5.0 | 15.0 | 3.0 | Microwave | 2 | >99 c |
aSubstrate (0.1 mmol), PdCl2(CH3CN)2 catalyst, sXPhos ligand 12, Cs2CO3 (2.5 eq.), phenylacetylene 16, CH3CN/H2O (1 : 1, 2 mL), sealed tube, 100 °C, solids and solvents purged with nitrogen.
bBased on ratio of starting material aromatic peak at δ H 6.50 ppm compared to product aromatic peak at δ H 6.56 ppm in CDCl3.
cBased on ratio of starting material aromatic peak at δ H 7.89 ppm compared to product aromatic peak at δ H 7.96 ppm in CD3OD.