Detailed examination of the 13C NMR spectra showed signals for two
quaternary carbons (δC 202.4 and 144.4) and an exomethylene
(δC 124.6) in the downfield region, replacing a quaternary
oxygenated carbon (δC 74.0), an oxymethine (δC 80.6), and a
methyl carbon (δC 25.0 or 26.0) in 17 (Table 3).