We investigate the thermally induced cyclization of 1,2-bis(2-phenylethynyl)benzene on Au(111) using scanning tunneling microscopy and computer simulations. Cyclization of sterically hindered enediynes is known to proceed via two competing mechanisms in solution: a classic C-1-C-6 (Bergman) or a C-1-C-5 cyclization pathway. On Au(111), we find that the C-1-C-5 cyclization is suppressed and that the C-1-C-6 cyclization yields a highly strained bicyclic olefin whose surface chemistry was hitherto unknown. The C-1-C-6 product self assembles into discrete noncovalently bound dimers on the surface. The reaction mechanism and driving forces behind noncovalent association are discussed in light of density functional theory calculations.