Structure bicyclic/tricyclic

There are several (sometimes interconvertible) cyclo-phosph(III)azanes, illustrated in Scheme 47. Bicyclic, tricyclic, adamantane cage, and more complex structures can be obtained by minor variations of the reaction conditions, also depending on the nature of the substituents at phosphorus and nitrogen sites. For reviews see Reference 214. 

The Lewis acid-promoted carbonyl-ene reaction of enantiomerically pure 4-oxoazetidine-2-carbaldehydes gave homoallylic alcohols, which have been used for the diastereoselective preparation of fused bicyclic, tricyclic and tetracyclic p-lactams of non-conventional structure 49 and 50, using tandem one-pot radical addition/cyclization or elimination-intramolecular Diels-Alder sequences <03JOC3106>. 

The diterpenoids, which contain 20 carbon atoms, are represented by acyclic, monocyclic, bicyclic, tricyclic, and tetracyclic structures. Over 5,000 naturally occurring diterpenoids, many of which frequently occur in plant families Araliaceae, Aster-aceae, Cistaceae, Cupressaceae, Euphorbiaceae, Leguminosae, Labiatae, and Pinaceae, are known (32). The acyclic diterpenoid... 

The fungus Penicillium rugulosum was isolated from the sponge Chondrosia reniformis collected off the island of Elba, Italy. Chemical investigation yielded a series of structurally unusual tricyclic and bicyclic pentaenes, pnigosenes A1 (2), A2 (3), A3 (4), B1 (5), B2 (6), Cl (7), and C2 (8). ... 

Cyclic adj. All cyclic compounds are recognized by their ring structure. Benzene is the simplest and most well-known cyclic compound, consisting of a single ring. Its monocyclic. When two or more rings are involved as with naphthalene, for example, the compound is bicyclic, tricycle, etc. Cyclic compounds may contain from three to six or more carbon atoms in the ring, e.g.. Cyclopropane - three atoms Cyclobutane -four atoms Cyclopentane - five atoms Cyclohexane - six atoms. 

Terpene synthesis in nature is a complex process involving successive electrophilic additions followed by a variety of skeletal rearrangements, including those of the Wagner-Meerwein variety. These reactions are typically catalyzed by enzymes and are responsible for the wide array of structural diversity in these compounds, including 6-6-6-5 tetracycles, 6-6-6-6-5 pentacycles, 6-6-6-6-6 pentacycles, and the less abundant acyclic, monocyclic, bicyclic, tricyclic, and hexacyclic triterpenoids. Each of the more than 100 triterpene skeletons identified in nature are formed through the involvement of several multifunctional triterpene synthases. 

Diterpenes are a structurally diverse class of C20 natural compounds, widely distributed in nature and originating by condensation of four isoprene units derived from mevalonate or deoxyxylulose phosphate pathways. The latter, recently discovered, originates the diterpene compounds in plants. Diterpenes can be classified as Unear, bicyclic, tricyclic or tetracyclic, pentacyclic, and macrocyclic diterpenes depending on their skeletal core. In nature, they are commonly found in a polyoxygenated form with keto and hydroxyl groups, these last often esterified by small-sized aliphatic or aromatic acids. 

Occasionally, addition products of 4//-l,2,4-triazole-3,5-diones or diazenedicarboxylic esters and oxepins have been obtained whose formation can be rationalized by an addition to the 2,4-diene system in the oxepin, e.g. formation of 10.190191 In these cases, the primary adduct usually cannot be isolated, because it undergoes a hetero-Cope rearrangement to a tricyclic or bicyclic structure in which the oxepin oxygen has become part of a carbonyl function.190 191,227... 

Of the fundamental nonalternant hydrocarbons, only two prototypes were known about fifteen years ago azulene (XI, Fig. 5), the molecular structure of which was determined by Pfau and Plattner and fulvene (XIX) synthesized by Thiec and Wiemann. Early in the 1960 s many other interesting prototypes have come to be synthesized. Doering succeeded in synthesizing heptafulvene (XX) fulvalene (XXI) and heptafulvalene (XXIII). Prinzbach and Rosswog reported the synthesis of sesquifulvalene (XXII). Preparation of a condensed bicyclic nonalternant hydrocarbon, heptalene (VII), was reported by Dauben and Bertelli . On the other hand, its 5-membered analogue, pentalene (I), has remained, up to the present, unvanquished to many attempts made by synthetic chemists. Very recently, de Mayo and his associates have succeeded in synthesizing its closest derivative, 1-methylpentalene. It is added in this connection that dimethyl derivatives of condensed tricyclic nonaltemant hydrocarbons composed of 5- and 7-membered rings (XIV and XV), known as Hafner s hydrocarbons, were synthesized by Hafner and Schneider already in 1958. 

The Robinson annulation is a valuable method for preparing bicyclic and tricyclic structures that can serve as starting materials for the preparation of steroids and terpenes.175 Reaction with 2-methylcyclohexan-l,3-dione gives a compound called the Wieland-Miescher ketone. 

Longifolene is a tricyclic sesquiterpene. It is a typical terpene hydrocarbon in terms of the structural complexity. The synthetic challenge lies in construction of the bicyclic ring system. Schemes 13.24 through 13.33 describe nine separate syntheses of longifolene. We wish to particularly emphasize the methods for carbon-carbon bond formation used in these syntheses. There are four stereogenic centers in longifolene,... 

There are only a few examples of bicyclic structures 194 described in the literature. On the other hand, similar tricyclic analogs containing one bridgehead nitrogen atom are not rare and some typical examples will be described here. 

A model study 92) showed that when the hemiacetal (268) was solvolyzed in formic acid, the bicyclic product (269) was isolated in good yield 92). This method was then used to synthesize the tricyclic nucleus of verrucarol (272)92). On reaction with pTsOH, the acetate (270) underwent rapid rearrangement to (271), which constituted part of the structural feature of verrucarol (272) 92K... 

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