Three's a crowd: The combination of a Brønsted acid and a hydrogen-bond donor cocatalyst was found to promote various ionic [2+4] cycloadditions under mild reaction conditions (see scheme; Ts=4-toluenesulfonyl). Thiophosphoramides are the most effective cocatalysts because of the stronger counterion activation effect resulting from three, rather than two, hydrogen bonds involved in anion binding.
No takes yet. Share an insight, caveat, or question.
Borovika et al. (2013) studied this question.
Synapse has enriched 5 closely related papers on similar clinical questions. Consider them for comparative context: