(30b). Subsequent condensation with tert-butyl2-lithiopropanoate gave, on acidification and hydrogenation over Rh/Al2O3, 32, which was formed with an 85: 15 diastereoselectivity. Alternative but less concise routes to 16a were explored. In addition, unsuccessful attempts to prepare nonactic acid (2a) from threo-pentanetriol (21a) were examined.