However, treatment of the substrate 201b with catalyst 213 afforded a 11:1 mixture
of the 6,5- and 5,6-benzannulated spiroacetals 204 and 203.
Deslongchamps et al. [109] have also applied their mercury(II) protocol to mono
(benzannulated) spiroacetals (Scheme 50). Thus, treatment of alkyne diol 201 with
catalytic Hg(OTf) 2 afforded the 6,6-spiroacetal 205 in excellent yield. The
THP-protected alcohol could also be used directly in the reaction with only a
small drop in yield.
2.6.4 Bis(benzannulated) Spiroacetals: Gold, Rhodium, and Iridium
Catalysts
For the bis(benzannulated) system 221, Ir(I)-catalyst 207 and Rh(I)-catalyst 209
were the most effective for the spirocyclization, with the reaction reaching 98 %
Fig. 4 Rh(I)- and Ir(I)-based catalysts that have found use in hydroalkoxylation reactions toward
spiroacetals
Synthesis of 5,6- and 6,6-Spirocyclic Compounds
225