There is a strong suggestion that Japan was being fed nuclear technology by the Germans throughout 1943-5. The capture of German supply submarines, and their contents, by the allies after the German surrender goes some way to making this look likely.
With the capture of U234 (Ironic name) There are reports that there was not only 560kg of unenriched uranium (a fact not reviled till after the end of the cold war) but also enough enriched uranium 234 to have helped build one of the two atomic devices dropped on Japan.
Hitlers motives for supplying the Japanese thus was to straighten them and distract the allies in the west allowing him more time to deal with the Soviets.
Now here's a question. If the Japanese had made a bomb, (the problem for the Japanese was not so much how to enrich uranium but rather getting their hands on enough of the stuff to make a bomb) what would the allies have done?
How would the Soviets have reacted to nuclear powers on either side of their country? Would the US have made nice with the Japanese so hem the USSR in?