A related, ring-rearrangement metathesis (RRM) strategy has been reported by
Blanchard and coworkers [193] for the synthesis of a variety of spiroacetals
(Scheme 98). Treatment of the oxabicycles 405 with second-generation Grubbs
catalyst initiated the RRM cascade, affording the unsaturated 5,6-spiroacetals 409
in excellent yields. The 6,6-spiroacetal 411 could also be accessed using the
oxabicyclo[3.2.1]octenone 410 as the substrate for the RRM.
The 6,5,6- and 6,6,6-bis-spiroacetals 413 and 415 could also be accessed by
substituting the TBS-protected alcohol with a second allyl substituent, allowing
sequential RRM–RRM reactions (Scheme 99). The 6,5,6-bis(spiroacetal) 413 was
obtained in moderate yield, while the yield of the 6,6,6-bis(spiroacetal) 415 was
much higher.
Scheme 96 RCM strategy in the synthesis of aigialospirol [191]
Scheme 97 RCM strategy in the synthesis of papulacandin-like spiroacetals [192]
Synthesis of 5,6- and 6,6-Spirocyclic Compounds
255
Blanchard and coworkers [193] for the synthesis of a variety of spiroacetals
(Scheme 98). Treatment of the oxabicycles 405 with second-generation Grubbs
catalyst initiated the RRM cascade, affording the unsaturated 5,6-spiroacetals 409
in excellent yields. The 6,6-spiroacetal 411 could also be accessed using the
oxabicyclo[3.2.1]octenone 410 as the substrate for the RRM.
The 6,5,6- and 6,6,6-bis-spiroacetals 413 and 415 could also be accessed by
substituting the TBS-protected alcohol with a second allyl substituent, allowing
sequential RRM–RRM reactions (Scheme 99). The 6,5,6-bis(spiroacetal) 413 was
obtained in moderate yield, while the yield of the 6,6,6-bis(spiroacetal) 415 was
much higher.
Scheme 96 RCM strategy in the synthesis of aigialospirol [191]
Scheme 97 RCM strategy in the synthesis of papulacandin-like spiroacetals [192]
Synthesis of 5,6- and 6,6-Spirocyclic Compounds
255