Here is an update to the Ugi synthesis. It turns out that 1-isocyanocyclohexene is tough to find commercially. I only identified a potential source from a German company. This problem was addressed in this paper,
The solution phase synthesis of diketopiperazine libraries via the Ugi reaction: Novel application of Armstrong's convertible isonitrile Christopher Hulme*, Matthew M. Morrissette, Francis A. Volz and Christopher J. Burns Tetrahedron Letters
Volume 39, Issue 10 , 5 March 1998, Pages 1113-1116
where they tried alternatives. Benzyl isocyanide seemed to work well and it is obtainable from Sigma-Aldrich fairly cheaply.