isomerized to the endocyclic isomer exclusively. Similarly, Pettus and coworkers
[154] were only able to obtain bis(benzannulated) spiroacetal 320 in poor yield
when using enol ether 318 as the dienophile. However, when the enol ether 322
(which is less prone to isomerization) is submitted to the same conditions,
paecilospirone-like spiroacetal 323 is obtained in moderate yield.
Thus, access to the rubromycin 5,6-bis(benzannulated) spiroacetal framework
would necessitate a different approach. One solution [165] has been to use more
stable benzofuranone-derived vinyl sulfoxides (e.g., 324) as the dienophile
(Scheme 79).
Scheme 78 HDA approaches toward bis(benzannulated) spiroacetals [154, 164]
Scheme 79 Xie et al.’s vinyl sulfoxide-based HDA approach toward bis(benzannulated)
spiroacetals [165]
244
M.A. Brimble and L.A. Stubbing
[154] were only able to obtain bis(benzannulated) spiroacetal 320 in poor yield
when using enol ether 318 as the dienophile. However, when the enol ether 322
(which is less prone to isomerization) is submitted to the same conditions,
paecilospirone-like spiroacetal 323 is obtained in moderate yield.
Thus, access to the rubromycin 5,6-bis(benzannulated) spiroacetal framework
would necessitate a different approach. One solution [165] has been to use more
stable benzofuranone-derived vinyl sulfoxides (e.g., 324) as the dienophile
(Scheme 79).
Scheme 78 HDA approaches toward bis(benzannulated) spiroacetals [154, 164]
Scheme 79 Xie et al.’s vinyl sulfoxide-based HDA approach toward bis(benzannulated)
spiroacetals [165]
244
M.A. Brimble and L.A. Stubbing