Using their imidophosphate dimer 121, unsubstituted dihydropyran and
dihydrofuran alcohols 130 gave the corresponding spiroacetals 129 in good yield
with excellent stereocontrol, favoring the contra-thermodynamic mono-anomeric
spiroacetal (Scheme 32). The thermodynamic spiroacetal could also be obtained
using ent-121 in comparable yield and enantioselectivity.
Scheme 31 Comparison of imidophosphate dimer 121 and (S)-TRIP for the spirocyclization of
enol ethers
Scheme 32 Use of imidophosphate dimer 121 for the spirocyclization of enol ethers [76]
Synthesis of 5,6- and 6,6-Spirocyclic Compounds
213