[GRAPHICS] 1,4-Butanediol has been used as the hydrogen donor in transfer hydrogenation reactions. The equilibrium is driven by the formation of gamma-butyrolactone, and the diol is therefore not required in excess.
Maytum, H. C., Tavassoli, B., & Williams, J. M. J. (2007). Reduction of aldehydes and ketones by transfer hydrogenation with 1,4-butanediol. Organic Letters, 9(21), 4387-4389. https://doi.org/10.1021/ol702029n