Table tricyclic derivatives from

In view of the remarkable stability of metal homoenolates of esters, the existence of homoenolate species containing a 3-halo substituent, i.e. zinc carbenoid moiety connected to an ester group, appeared to be possible. Indeed, when a silyl ketene acetal is treated with a carbenoid generated from CHBrj and Et2Zn, two types of highly intriguing reactions ensue [58]. With a purely aliphatic substrate, Eq. (61), an alkyl cyclopropylcarboxylate due to intramolecular p-CH-insertion of the intermediate zinc carbenoid formed. When the substrate contained an olefmic double bond in the vicinity of the carbenoid function, Eq. (62), in particular an intermediate derived from an a,P-unsaturated ester, internal cyclo-propanation occurred to give bicyclic or tricyclic product (Table 15). 

The cycloadditions of several unusual oxyallyl cations are briefly outlined in Table 1. Tricyclic oxa-bridged substrates can be readily assembled from cyclic oxyallyl cations derived from monohalogenated cyclic ketones 14 a and LiClO/EtjN (entry 1) [30]. Dihalogenated cyclic ketones 14b can also serve as cyclic oxyallyl cation precursors when treated with diiron nonacarbonyl [31], or zinc-copper couple [32]. Cycloadditions of this type have been successful in producing oxatricyclic compounds where n = 2,3,4,5,9, although some adducts are mixtures of cis and trans isomers. 

Various bi- and tricyclic diterpenes are derived from the monocyclic cembrane (Table 4). Casbane, for example, is simply 2,15-cyclocembrane another bond between C-6 and C-10 leads to lathyrane, from which the iatrophanes arise by opening the C-l-C-2 bond. 

Benzonitrile reacts similarly with a-oxoketenes to give the [4-f2] cycloadducts Linear and cyclic azomethines also form 1 2 cycloadducts with ketenes. The initially formed ionic 1 1 adduct reacts with another equivalent of the ketene to give the [4-1-2] cycloadduct. The total reaction is a [2- -2- -2] cycloaddition reaction. The [2-F2-F2] cycloadducts derived from azomethines and ketenes are listed in Table 4.12. In the reaction of ketene or diketene with heterocyclic compounds the so-called Wollenberg compounds are obtained. For example, from quinoline and ketene the tricyclic compound 410 is obtained (see Table 4.12). 

West also demonstrated that oxyallyls derived from pyran-4-ones can participate in electrophilic aromatic substitution reactions. Irradiation of pyran-4-ones 34 with aryl groups appended in the 2-position produced tricyclic tetrahydrobenz[e]indenone 35 in fair to moderate yield (Table 81.4). Capture of the oxyallyl intermediate by solvent and Type A rearrangement to pyran-2-ones competed with the desired intramolecular EAS reaction. Interestingly, the yield of 35 was concentration dependent (higher yields with dilution). It is not clear how concentration affects the bifurcation of the oxyaUyl intermediate between intramolecular trapping and rearrangement. 

In the case of electrophilic addition, the reactions of tricyclic dienes 1 with several electrophilic reagents have been investigated.1 7 Interestingly, some of these compounds undergo addition reactions with remarkable syn stereoselectivity. For example, the reaction of dimethyl tricy-clo[4.2.2.02,5]deca-3,9-diene-7,8-dicarboxylate with iodine azide solution, prepared in situ from an excess of sodium azide and iodine monochloride, in acetonitrile at — 5 C provided the. yyn-4-azido-3-iodo derivative 2 (Table 1) in 90% yield.1,2,4,6 The formation of the 5,>,n-4-azido-3-iodo derivative 2 is thought to be the first example of a syn addition of iodine azide to an alkene.1,2 The formation of the syn-product is best explained by the twist strain theory,8 according to which the syn transition structure A is favored over the an/7-coplanar transition structure B.1... 

Electron densities obtained from molecular orbital calculations on thieno- and pyrrolo-fused derivatives are listed in Table XXIII (Part B). Similar values were obtained with furo- and isoxazolotropylium salts 218, 333, and 329 (Section III,B,2,b). In the field of tricyclic compounds, electron densities of furothieno-fused (237a, 238a) and bisthieno-fused ions (237b, 238b Scheme 57) were calculated (73ACS2257). 

Table 1 lists the experimental conditions for the electrochemical formation of a cyclopropyl ring from a variety of 1,3-dihaloalkanes, mostly from dibromoalkyl derivatives. A free cyclopropyl ring as well as a spiro derivative (entry 6), bicyclobutanes (entries 8-10) and other fused and highly strained systems such as tricyclene (entry 11) and a propellane derivative (entries 12,13) were obtained. In addition, Carroll and Peters have found evidence for the intermediacy of [2.2.1 ]propellane upon reducing 1,4-dihalonorbor-nanes electrochemically at a low temperature, although attempts to isolate it were unsuccessful. The intramolecular electrochemical reduction of a dihalo-substituted tricyclic compound leads to cyclization with formation of a tetracyclic derivative in which... 

The two aromatic groups noted in several of the classes of antihistamines can be connected to each other through additional atoms (e.g., heteroatoms like sulfur or oxygen) or through a short, 1- or 2-carbon chain. They have a general structure shown in Figure 37.11. The earliest potent tricyclic antihistamines (Table 37.7) were phenothiazines (Y=S, X=N). The phenothiazine antihistamines contain a 2- or 3-carbon, branched alkyl chain between the nonbasic phenothiazine nitrogen and the aliphatic amine. They differ from the antipsychotic phenothiazine derivatives in which the chain usually is three... 

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