Thus, AgOTf-catalyzed cycloisomerization of alkyne diol 300 gives the
dienophile, while cycloisomerization of aldehyde 301 generates the o-QM. Cycloaddition of 302 and 303 then affords the 5,6-spiroacetal core 304, which is isolated
after hydrogenation of the double bond in 83 % yield as a 2:1 mixture of
diastereomers.
Similarly, based upon the proposed union of two naturally occurring components, De Brabander et al. [162] have also used a Ag-initiated cycloisomerization/
dearomatization/cycloaddition cascade for the synthesis of 96 (Scheme 76).
Scheme 73 Pettus et al.’s HDA approach toward berkelic acid [159]
Scheme 74 Fan ˜ana ´s et al.’s Pd-catalyzed HDA cascade approach toward spiroacetals [160]
Synthesis of 5,6- and 6,6-Spirocyclic Compounds
241
dienophile, while cycloisomerization of aldehyde 301 generates the o-QM. Cycloaddition of 302 and 303 then affords the 5,6-spiroacetal core 304, which is isolated
after hydrogenation of the double bond in 83 % yield as a 2:1 mixture of
diastereomers.
Similarly, based upon the proposed union of two naturally occurring components, De Brabander et al. [162] have also used a Ag-initiated cycloisomerization/
dearomatization/cycloaddition cascade for the synthesis of 96 (Scheme 76).
Scheme 73 Pettus et al.’s HDA approach toward berkelic acid [159]
Scheme 74 Fan ˜ana ´s et al.’s Pd-catalyzed HDA cascade approach toward spiroacetals [160]
Synthesis of 5,6- and 6,6-Spirocyclic Compounds
241