Iridoids synthesis

H. Hashimoto, K. Furuichi, and T. Miwa, Cyclopentane annelated pyranosides A new approach to chiral iridoid synthesis, J. Chem. Soc. Chem. Commun. p. 1002 (1987). 

The enviromental changes can also affect to the iridoids synthesis. In vitro studies with Plantago lanceolata, the levels of iridoids were increased with warm temperatures, between 18-20 °C, and were decreased by low light intensity or high nitrogen levels [19-21], The UV-B radiation did not affect to the iridoids production [22],... 

Hoye and Richardson have published an ingeneous synthesis of the tricyclic iridoid sarracenin (170) which relied on the Paterno-Buchi cycloaddition between acetaldehyde and cyclopentadiene as the intial step (Scheme 38)79. This reaction provided a 5 1 mixture of adducts 166a and 166b. The major adduct was opened with camphor-10-sulfonic acid (CSA) in methanol and the alcohol was tosylated to give 167. Displacement with malonate 168 and decarboalkoxylation/demethylation steps gave 169. Ozonolysis, reductive workup and acid-catalyzed acetalization then furnished 170. 

The facile conversion of carbonyl groups into lactones via cyclobutanones offers many opportunities for synthetic applications considering the importance of butanol-ides in natural products synthesis. The iridoids vividly illustrate this potential. Allamandin (163) 135 c) and its dehydrated relative plumericin (164) 135 d), compounds possessing antifungal, antibacterial, and antitumor activity, pack a great deal of... 

The full paper on the synthesis of onikulactone and mitsugashiwalactone (Vol. 7, p. 24) has been published.Whitesell reports two further useful sequences (cf. Vol. 7, p. 26) from accessible bicyclo[3,3,0]octanes which may lead to iridoids (123 X=H2, Y = H) may be converted into (124) via (123 X = H2, Y = C02Me), the product of ester enolate Claisen rearrangement of the derived allylic alcohol and oxidative decarboxylation/ whereas (123 X = 0, Y = H) readily leads to (125), a known derivative of antirride (126) via an alkylation-dehydration-epoxi-dation-rearrangement sequence. Aucubigenin (121 X = OH, R = H), which is stable at —20°C and readily obtained by enzymic hydrolysis of aucubin (121 X = OH, R = j8-Glu), is converted by mild acid into (127) ° with no dialdehyde detected sodium borohydride reduction of aucubigenin yields the non-naturally occurring isoeucommiol (128 X=H,OH) probably via the aldehyde (128 X = O). ... 

A striking example of the power of A -heterocyclic carbene (NHC)-bearing catalysts with sterically demanding substrates was disclosed by Chavez and Jacobsen, " who presented a route to several iridoid natural products, exemplified by the enantio- and diastereoselective synthesis of boschnialactone 31 outlined in Scheme 5. Chiral aldehyde 27, available from citronellal by Eschenmoser-methylenation in a single step, reacted despite the presence of an isoprenyl moiety and a gi OT-disubstituted double bond, in the presence of catalyst C smoothly to form... 

Since neonepetalactone is closely related to the iridoids described above, the total synthesis followed the same procedure (Scheme 1.2.14) leading to the desired natural product in 55% overall yield and excellent de and ee values of >96%. 

Iridium nanoparticles, preparation, 12, 82 Iridium(III) O-ligated complexes, preparation, 7, 315 Iridium polyhydrides, preparation and characteristics, 7, 405 Iridium pyrrolyl derivatives, reactivity, 7, 282 Iridium tetrahydrides, characteristics, 7, 407-408 Iridium trihydrides, preparation, 7, 405 Iridium vinylidenes, synthesis and characteristics, 7, 352 Iridium xyliphos complexes, properties, 7, 442 Iridoids, via Pauson-Khand reaction, 11, 360 Iron(arene) (cyclopentadienyl) cations, preparation and reactivity, 6, 166... 

I. Marco-Contelles and J. Ruiz-Caro, Iridoids from carbohydrates via Pauson-Khand reaction synthesis of advanced highly oxygenated cyclopentane-annulated pyranosides from D-glucal derivatives,. /. Org. Chem., 64 (1999) 8302-8310. 

The use of enol ethers as dienophiles improves the reaction, however, still high temperature is needed and endo/exo-selectivity is low. Thus, cycloaddition of ethyl vinyl ether 2-83 to cyclopentenecarbaldehyde 2-82 gave the cycloadduct 2-84 as a 1 1 mixture which was used for the synthesis of iridoids (Fig. 2-23) [121]. 

The methyl-substituted BCR is useful for the construction of some iridoid cyclopentanoids. Keto alcohol (137), a crucial intermediate for a synthesis of ( )-chrysomelidial (138), can be prepared from the cycloadduct (108) of cyclopentenone and the methyl-TMM synthon (equation 145)7 This expedient approach to the keto cohol, four steps and 83% overall yield from the bifunctional reagent (107), is a considerable improvement over a previous 14-step sequence using conventional methodologies. Although the initial bicyclic ketone (108) is a 1 1 epimeric mixture, base-catalyzed equilibration of the products from ozonolysis results in only one epimer, having the required stereochemistry. This... 

SCHEME 4.48 Synthesis of iridoid glycoside using silyl ether. 

Tietze, L-F, Fischer, R, Iridoids.l9. Stereoselective synthesis of iridoid glycosides, Angew. Chem. Int. Ed. Engl, 22, 888, 1983. 

Another example of the usefulness of tri-O-acetyl-D-glucal in the preparation of a complex target in optically pure form is illustrated by the synthesis of iridoids. 

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