Iridoid hemiacetal

Simple iridoids are volatile iridoids of which the best known is the cat-exciting nepetalactone (C5 C50L) from Nepeta cataria (catnip) (Lamiaceae). The lactone nepetalactone, the hemiacetal neomatatabiol (G51G50H), iridodiol (in the ring opened bi-aldehyde... 

Analogous to the hemiacetals, anomeric silyl ethers can also serve as glycosyl donors. Glycosyl silyl ethers were first used as glycosyl donors to glycosylate acetals of carbonyl compounds [537-540]. Thus, the iridoid glycoside 255 was obtained by glycosylation of the acetyl derivative... 

Similarly, methyl diformylacetate, a /(-tricarbonyl compound, is almost totally enolized towards the aldehyde and reacts smoothly with alkenes to give a hemiacetal structure 7 present in many of the iridoid glucosides113-116. 

An alternate approach to the iridoid core, again developed by Biichi, utilized the [2+2] cycloaddition of cyclopentene 28 and tricarbonyl 29 (Scheme 6). Following photochemical annulation, the resulting cyclobutane 30 underwent a retro-aldol reaction and hemiacetal formation to provide racemic cyclopenta[c]pyran 31. Elaboration of 31 to loganin (16) required 10 additional steps. ... 

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