Structure tricyclic

Transesterification reactions provide an applicable synthetic route to the preparation of organometallic compounds with unusual structures. Tricyclic organometallic compounds, which have the general formula... 

Polycyclic compounds are those that contain more than one ring. The lUPAC classifies polycyclic structures according to the minimum number of bond cleavages required to generate a noncyclic structure. The structure is bicyclic if two bond disconnections yield an open-chain structure, tricyclic if three, tetracyclic if four, and so on. Adamantane, a naturally occurring hydrocarbon found in petroleum, for example, is tricyclic because three bond cleavages are needed before an open-chain structure results. 

The alkaloid vasicine was first isolated from Adhatoda vasica in 1925 but the structure (996) was elucidated only after a great amount of work, culminating in two independent syntheses in 1935 (B-53MI21301). It was made subsequently by a simple route from 2-aminobenzaldehyde and 4-amino-2-hydroxybutyraldehyde (994) followed by dehydration of the tricyclic intermediate (995) (60TL(25)44>. Vasicine has bronchodilatory activity of a low order. Two related unnamed alkaloids (997) and (998) were obtained in 1965 from members of the Araliaceae family, viz. Mackinlaya subulata and M. macrosciadia both had been synthesized earlier (66AJC151). 

Treatment of the alcohol whose structure is shown here with sulfuric acid gave as the major organic product a tricyclic hydrocarbon of molecular formula CigHig. Suggest a reasonable structure for this hydrocarbon. 

Reaction of nitro-2f/-chromene derivatives 134 with 135 in methanol at room temperature afforded a mixture of the Z-isomer 136 and tricyclic compound 137, which could be formed by denitrocyclization reaction of the corresponding primarily formed E-isomer and the following dehydrogenation (Eq. 15). The structural identification was based on the MS and H-NMR, however, it is not sufficiently documented and similar examples are not known (91IJC(B)297). 

Revised structures have been proposed for these compounds. The brownish-yellow acid obtained with maleic anhydride has been shown by ultraviolet, infrared, and nuclear magnetic resonance absorption measurements and oxidative degradation to have the tricyclic structure... 

Intramolecular cycloadditions of substrates with a cleavable tether have also been realized. Thus esters (37a-37d) provided the structurally interesting tricyclic lactones (38-43). It is interesting to note that the cyclododecenyl system (w = 7) proceeded at room temperature whereas all others required refluxing dioxane. In each case, the stereoselectivity with respect to the tether was excellent. As expected, the cyclohexenyl (n=l) and cycloheptenyl (n = 2) gave the syn adducts (38) and (39) almost exclusively. On the other hand, the cyclooctenyl (n = 3) and cyclododecenyl (n = 7) systems favored the anti adducts (41) and (42) instead. The formation of the endocyclic isomer (39, n=l) in the cyclohexenyl case can be explained by the isomerization of the initial adduct (44), which can not cyclize due to ring-strain, to the other 7t-allyl-Pd intermediate (45) which then ring-closes to (39) (Scheme 2.13) [20]. While the yields may not be spectacular, it is still remarkable that these reactions proceeded as well as they did since the substrates do contain another allylic ester moiety which is known to undergo ionization in the presence of the same palladium catalyst. 

The importance of the 1,3-dipolar cycloaddition reaction for the synthesis of five-membered heterocycles arises from the many possible dipole/dipolarophile combinations. Five-membered heterocycles are often found as structural subunits of natural products. Furthermore an intramolecular variant makes possible the formation of more complex structures from relatively simple starting materials. For example the tricyclic compound 10 is formed from 9 by an intramolecular cycloaddition in 80% yield ... 

Historically, both the tricyclic antipsychotic and antidepressant agents are derived in almost direct line from a series of tricyclic antihistaminic compounds (see 104 below). Minor changes in structure in some of the newer... 

The very slow onset of action and side effects which follow from the anticholinergic side effects characteristic of the tricyclic antidepressants has led to a continuing effort to find replacements from other structural classes which might thus be devoid of this defect. A series of alkoxy phenylpropylamines has been investigated extensively in this search for non-tricyclic antidepressants. The most recent analogue, tomoxetine (69), is accessible by the same route [15] used to prepare the earlier analogue, nisoxetine, in which methoxyl replaces the ortho methyl group. 

Most of the widely used antidepressants are tricyclics related to imipramine. A 1-phenyltetrahy-droisoquinoline analogue, nomifensine (60), departs from this structural pattern. Hiarmacologi-cally it inhibits the reuptake of catecholamines such as dopamine at neurons. It can be synthesized by alkylation of 2-nitrobenzyl-methylamine with phenacyl bromide followed by catalytic reduction of the nitro group (Pd-C) and then hydride reduction of the keto moiety to give 59. Strong acid treatment leads to cyclodehydration to nomifensine (60) [17]. 

The pharmaceutical interest in the tricyclic structure of dibenz[6,/]oxepins with various side chains in position 10(11) stimulated a search for a convenient method for the introduction of functional groups into this position. It has been shown that nucleophilic attack at the carbonyl group in the 10-position of the dibenzoxepin structure renders the system susceptible to water elimination. Formally, the hydroxy group in the enol form is replaced by nucleophiles such as amines or thiols. The Lewis acids boron trifluoride-diethyl ether complex and titanium(IV) chloride have been used as catalysts. 

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... 

Irradiation of 3,6-bridged oxepins with ester functions in the 4- and 5-positions gives tricyclic structures 3 in which the oxepin oxygen becomes part of an aldehyde function.248-250 When chiral esters are used, it has been shown that the irradiation in solid state proceeds with a high degree of diastereoselectivity.249,251,252... 

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