Terpenoid intermediates synthesis

Intermolecular.- Reviews have described some of the photochemical (2+2)-cycloaddition reactions of enones used in the synthesis of natural products. Other reports have also focussed on such additions as key steps in the design of natural products. Thus the photoadducts obtained by the cycloaddition of the enone (61) to the alkene (62) have been used as the starting materials for the synthesis of terpenoid intermediates. ... 

Since GAs as diterpenes share many intermediates in the biosynthetic steps leading to other terpenoids, eg, cytokinins, ABA, sterols, and carotenoids, inhibitors of the mevalonate (MVA) pathway of terpene synthesis also inhibit GA synthesis (57). Biosynthesis of GAs progresses in three stages, ie, formation of / Akaurene from MVA, oxidation of /-kaurene to GA 2" hyde, and further oxidation of the GA22-aldehyde to form the different GAs more than 70 different GAs have been identified. 

As exemplified in the present procedure, the reaction has been optimized and extended in scope it affords functionalized benzocyclobutenes as well as substituted isoquinolines in high yields. Benzocyclobutenes have been used as intermediates in the synthesis of many naturally occurring alkaloids, - steroids,polycyclic terpenoids,and anthracycline antibiotics. The traditional routes leading to the preparation of benzocyclobutenes have been... 

Snider and colleagues have developed the sequential ene reaction/thia-[2,3]-Wittig reaction which provide appropriately functionalized product 152 at allylic position on simple alkene 150 in two steps involving intermediate 151 (equation 87) . Thia-[2,3]-Wittig rearrangement was often utilized as a key step of natural product synthesis. Masaki and colleagues have demonstrated that the potassium enolate thia-[2,3]-rearrangement of aUyl sulfide 153 to 154 is useful for the synthesis of terpenoid diol component 155 of the pheromonal secretion of the queen butterfly (equation 88) . 

Polyene cyclizations have been of substantial value in the synthesis of polycyclic natural products of the terpene type. These syntheses resemble the processes by which terpenoid and steroidal compounds are assembled in nature. The most dramatic example of biological synthesis of a polycyclic skeleton from a polyene intermediate is the conversion of squalene oxide to the steroid lanosterol. In the biological reaction, the enzyme presumably functions not only to induce the cationic cyclization but also to bind the substrate in a conformation corresponding to the stereochemistry of the polycyclic product.21... 

Easily available advanced synthons, such as the carbohydrates, amino acids, hydroxyacids, and terpenoids, make the synthetic task easier than the complexity metrics of the target suggests this is especially true for the glycosides, if the carbohydrate portion can be introduced intactly. It must also be borne in mind that the S metric is counted in a linearly additive hion, neglecting interactions between the functional groups (Whitlock 1998) such interactions are not treated adequately by any method so far proposed to calculate the molecular complexity. Moreover, no attention was paid here to the graphic analysis of the synthesis plan based on the molecular complexity of the intermediates these aspects have recently been reviewed (Bertz 1993 Whitlock 1998 Chanon 1998). 

Methyl-5-hepten-2-one is an important intermediate in the synthesis of terpenoids. Its odor properties are not impressive. It occurs in nature as a decomposition product of terpenes. Tagetone [6752-80-3] is a major component of tagetes oil. Solanone [1937-45-8] and pseudoionone [141-10-6] are acyclic Cn ketones with a terpenoid skeleton. Solanone is one of the flavor-determining constituents of tobacco, pseudoionone is an intermediate in the synthesis of ionones. 

The reaction of a bis-alkynic alcohol (103) with aqueous dimethylamine gives dimethyl-aminofuran (104) (74IZV206). trans-Enynols cyclize presumably through a cis intermediate with base (75RTC70) or mercury(II) sulfate, a method used for the synthesis of the terpenoid bilabone (105) (69JOC857). 

J. A. Bacigaluppo, M. I. Colombo, M. D. Preite, J. Zinczuk, E. A. Ruveda, The Michael-Aldol Condensation Approach to the Constmction of Key Intermediates in the Synthesis of Terpenoid Natural Prod-ucts, Pure Appl. Chem. 1996, 68, 683. 

Deaminomethylation of terpenoid Mannich bases is frequently applied (Table 23, Chap. II, A.2) in order to create an unsaturated moiety in the molecule. The reaction has been carried out on the Mannich bases of c7.v-4-caranone, 2-pinene-4-one and sesquiterpene lactones, the.se last compounds being intermediates in the synthesis"- of tumor inhibitors vemolepin and vemomenin, which have a structure of typ 491. 

Termite soldiers produce a large number of different chemical defense agents. Several of these molecules are unusual bioactive terpenoids such as the secotrinervitanes that have been isolated and their structure elucidated. In the laboratory of T. Kato, the total synthesis of (+)-3a-acetoxy-7,16-secotrinervita-7,11-dien-15P-ol was accomplished. The Nagata hydrocyanation was used to introduce a carbon at the P-position of a macrocyclic enone intermediate. The substrate was treated with excess diethylaluminum cyanide in dry toluene and the addition resulted in the formation of a 1 1 mixture of diastereomers, which could be readily separated by column chromatography. The cyano group was later converted to the corresponding methyl ester. 

Terpenes are flammable unsaturated hydrocarbons, existing in liquid form. They are found in essential oils, resins or oleoresins. They are used as intermediate for the synthesis of sesquitrepenes and terpenoids. They are classified as mono, di or triterpenoids. 

Some other products of interest are pseudoionones [54, 243, 260] and methyl pscudoionones [181], resulting from aldol condensation between citral and acetone or methyl ethyl ketone, respectively Fij ttre 16). Subsequent cyclalion of (methyl) pseudoionones over acid catalysts yields (methyl) ionones. lonones are cyclic terpenoids which have extensive uses as medicinal products, fragance materials and as intermediates in vitamin A synthesis. 

Azadirachtin (618), a terpenoid with strong antifeedant activity, possesses a unique bicyclic acetal subunit. Retrosynthetic analysis indicates that the intermediate 619 would be a suitable candidate for use in a convergent synthesis of the natural product. 

Crombie s group has also discussed the biogenesis of these monoterpenoids, giving examples of the various possibilities of the scission of the chrysanthemyl skeleton to the other skeletons, including the synthesis of the dehydrolavandulol (67) from a n s-chrysanthemic diol (68). They report some feeding experiments with C-labelled chrysanthemate, but incorporation into artemisia ketone was very low. The synthesis of a cyclopropyl terpenoid once discussed by Robinson as a possible biogenetic intermediate to artemisia ketone has been accomplished from nerol oxide it is discussed in the section on pyranoid monoterpenoids (below). 

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