Search forb→utransitions in exclusive hadronicB-meson decays

From a data sample of 242 000 BB\ifmmode\bar\else\textasciimacron\fi{} pairs collected with the CLEO detector at the \ensuremath{\Upsilon}(4S) resonance, we set upper limits for the branching ratios for exclusive hadronic decays of B mesons arising from b\ensuremath{\rightarrow}u transitions. Model-dependent limits for the ratio of the Kobayashi-Maskawa matrix elements ${V}_{\mathrm{ub}}$/${V}_{\mathrm{cb}}$ are presented.