text: Inspired by enzymes with deep active site pocket, List and coworkers designed and constructed a set of confined Bronsted acids with an extremely sterically demanding chiral pocket based on a C-symmetric bis(binapthyl) imidodiphosphoric acid. Within the chiral microenvironment, the catalysts has a geometrically fixed bifunctional active site that activates both an electrophilic part and a nucleophilic part of a substrate. This catalyst enables stereoselective spiroacetal formation with high enantiomeric excess for a variety of substrates.