patent has been registered for the process as early as 1974. See also Cryptophane References Cram, D. J.; Tanner, M. E.; Thomas, R., The taming of Cyclobutadiene Angewandte Chemie International Edition Volume 30, Issue 8, Pages 1024 - 1027 1991 Abstract Stabilization of Reactive Organometallic Intermediates Inside a Self-Assembled Nanoscale Host Dorothea Fiedler, Robert G. Bergman, Kenneth N. Raymond Angewandte Chemie International Edition Volume 45, Issue 5, Pages 745 - 748 2006 Abstract Supramolecular chemistry