Methyl 3-{4-[2-(4-hydroxy-1-oxocyclohexa-2,5-dienyl)-1H-indol-1-ylsulf-onyl]phenyl}propanoate (prepared)
Trimethyltin hydroxide (Strem; as received)
1,2-Dichloroethane (as received)

A mixture of the methyl ester (0.132 g; 0.3 mmol) and trimethyltin hydroxide (0.300 g; 1.7 mmol) in 1,2-dichloroethane (3 mL) was heated in a sealed vial under microwave conditions at 120 ^oC for 0.5 h, (with cooling air on). The cooled mixture was allowed to stand until a precipitate formed, then filtered, concentrated in vacuo and purified by column chromatography (EtOAc) to yield the carboxylic acid (0.051 g; 39%)

This method was tried after many other routes to the carboxylic acid from the methyl ester and t-butyl ester had failed. The final product passed CHN analysis, and looked pure by NMR, but a similar analogue (fluorinated in the 6- position of the indole) failed to give sufficiently accurate microanalysis, so tin contamination may be a problem. The original paper performed the reaction at 80 (not in a microwave). I did not attempt thermal conditions. Shortening the time, or using less trimethyltin hydroxide gave incomplete conversion in my hands. After heating, the reaction vessel was allowed to stand until tin compounds precipitated. The time taken varied, and sometimes was overnight. A yield of 65% was obtained for the 6-fluoro analogue, on 3x the scale (by performing the reaction 3 times, and combining the crude mixtures).

2.63 (2H, t, J = 7.5), 2.93 (2H, t, J = 7.5), 5.48 (1H, s, OH), 6.32 (2H, d, J = 10.3), 6.78 (1H, d, J = 0.3), 7.20-7.32 (4H, m), 7.42 (1H, d, J = 7.7), 7.56 (2H, d, J = 10.3), 7.78 (2H, d, J = 8.5), 7.99 (1H, d, J = 8.4).

A. J. McCarroll, T. D. Bradshaw, A. D. Westwell, C. S. Matthews, M. F. G. Stevens, J. Med. Chem., 2007, 50, 1707.

K. C. Nicolaou, A. A. Estrada, M. Zak, S. H. Lee, B. S. Safina, Angew. Chem. Int. Ed. 2005, 44, 1378-1382.