In this talk we showed how the yields of the unstable nuclei Ti44 and Ni56 depend on the initial mass, metallicity and rotational velocity. The main result is that non rotating models are still not able to produce a sufficient amount of Ti44 as required by the observations of the supernova remnant Cas A and 1987A, falling short by a factor four or five. Vice versa a few rotating models develop an extended O convective shell in which a significant amount of Ti44 is produced hydrostatically and preserved during the explosion. Though also in this case not enough Ti44 is synthesized, falling short by a factor of two or so, the possible contribution of an extended O burning shell on the global synthesis of this nucleus should be taken into account.