We study scheduling problems in bufferless time slotted WDM optical interconnects with wavelength conversion ability. We consider the case when the connection requests have different priorities and give algorithms that are a ware of the quality of service (QoS) requirements. The wavelength conversion considered in this paper is the general case of limited range wavelength conversion with arbitrary wavelength conversion capability, as limited range wavelength conversion is easier to implement and more cost effective than full range wavelength conversion, and it also includes full range wavelength conversion as a special case. We show that the problem of maximizing network throughput and giving service differentiation can be formalized as finding an optimal matching in a weighted bipartite graph. We then give an optimal distributed scheduling algorithm called the Downwards Expanding algorithm that runs in O(k2) time to find such a matching, where k is the number of wavelengths per fiber.