TCN and TCND Monomer Synthesis. Quadricyclane was prepared by photochemical isomerization of norbornadiene in batches of up to 17 g and yields up to >90% (Supporting Information Section 2). Heating quadricyclane in the presence of maleic anhydride gave TCN exo-anhydride 1 as a mixture of anti and syn diastereomers (67:33 anti:syn) in quantitative yield (Figure ). Crystallization led to enrichment of the anti-1 to 78:22 anti:syn (69% yield); further isolation of pure diastereomers was conducted following a subsequent synthetic step.