Werz et al. [195] have reported the synthesis of unsaturated spiroacetals 422 via
intramolecular ring opening of spirocyclopropanes 421 (Scheme 103). Oxidation of
the alcohol and subsequent acid-catalyzed ring opening affords the spiroacetals 422
in low to good yield.
Shair and coworkers [123] have reported a NBS-promoted intramolecular cyclopropane ring opening for the synthesis of the eastern half of cephalostatin 1
(Scheme 104).
Treatment of the cyclopropane 427 with NBS induced attack of the primary
alcohol onto the cyclopropane, giving the bromomethylene spiroacetal 428 as the
product. Subsequent reductive removal of the bromide and protection of the
Scheme 102 Cyclopropane ring opening for the synthesis of spiroacetals
Scheme 103 Intramolecular ring opening of a cyclopropane for the synthesis of spiroacetals [195]
258
M.A. Brimble and L.A. Stubbing
intramolecular ring opening of spirocyclopropanes 421 (Scheme 103). Oxidation of
the alcohol and subsequent acid-catalyzed ring opening affords the spiroacetals 422
in low to good yield.
Shair and coworkers [123] have reported a NBS-promoted intramolecular cyclopropane ring opening for the synthesis of the eastern half of cephalostatin 1
(Scheme 104).
Treatment of the cyclopropane 427 with NBS induced attack of the primary
alcohol onto the cyclopropane, giving the bromomethylene spiroacetal 428 as the
product. Subsequent reductive removal of the bromide and protection of the
Scheme 102 Cyclopropane ring opening for the synthesis of spiroacetals
Scheme 103 Intramolecular ring opening of a cyclopropane for the synthesis of spiroacetals [195]
258
M.A. Brimble and L.A. Stubbing