Naphthalene conjugated derivatives

Mai ins et al. (15) showed by TLC that rainbow trout exposed to l C-labeled naphthalene excrete 1-naphthyl glucuronic acid in the urine almost exclusively. Only 1% of the total radioactivity of the urine was in the form of non-conjugated derivatives. 

HPLC studies on the brain of mature rainbow trout revealed essentially four metabolites, including the dihydrodiol and 1-naphthol (12). No evidence was found for the presence of conjugated derivatives. It was concluded that the conjugated derivatives of naphthalene were excluded by blood-brain barrier systems that develop in mature organisms. 

A limited amount of information is available on the formation of metabolites of aromatic hydrocarbons in aquatic invertebrates however, some studies have elucidated the structures of conjugated and non-conjugated derivatives produced in these organisms. The bioconversion of naphthalene by the spider crab (Maia squinado) has been studied by Corner et al. (45). These workers identified... 

The typical red shifts on ring annelation are seen in 4,5-benzo-6-azaindole (45), which like 6-azaindole show a red shift of ca. 20 m/x in acid solution. The spectra of several substituted derivatives of this pyrroloquinoline are reported also, including the [2,3-a]naphthalene compound which has a max at 405 m/x. The other Tr-conjugated derivatives all have bands at long wavelength, and are assigned the band positions indicated. The methylene malonate compound shows a four-band spectrum, with the /S band at 225 mfi. 

Naphthalene (49) reacts with sodium in liquid ammonia to form a red complex which is quenched by methanol to form the 1,4-dihydro derivative (51), and may therefore be assumed to be the dianion (50).- If alcohol is present in the reaction mixture, then the 1,4,5,8-tetrahydro derivative (52) is formed (Scheme 6). 1-Naphthyl derivatives are reduced in the unsubstituted ring, whereas there is a maiked preference for reduction of the substituted ring in 2-methyl- and 2-methoxy-substituted isomers. This preference is not as well defined for bulkier substituents, however, and is reversed in the case of 2-f-butylnaphthalene further details are in a 1970 review. Because of the facile isomerization of the 1,4-dihydro isomers to conjugated derivatives, overreduction occurs readily and ether groups are fairly readily hydrogenolyzed. It is therefore important to select the reaction conditions with care.- ... 

The role played by dihydrodiols in the metabolic formation of phenols and their conjugated derivatives from aromatic substances is at present undecided. In theory, upon dehydrating a dihydrodiol, the phenolic hydroxyl should remain at that carbon most activated toward electrophilic substitution (14,625). This criterion of mechanism is satisfied in some instances (i.e., the halogenobenzenes (379, 682) and benzonittile (681). Furthermore, compounds that arise from the metabolism of aromatic hydrocarbons also arise from metabolism of dihydrodiols which are formed from them (94,163). However, hver slices and Uver microsomes capable of forming dihydrodiol from naphthalene form neg%ible amounts of naphthol (95,558). 

The versatility of poly(phenylcne) chemistry can also be seen in that it constitutes a platform for the design of other conjugated polymers with aromatic building blocks. Thus, one can proceed from 1,4- to 1,3-, and 1,2-phenylene compounds, and the benzene block can also be replaced by other aromatic cores such as naphthalene or anthracene, helerocyclcs such as thiophene or pyridine as well as by their substituted or bridged derivatives. Conceptually, poly(pheny ene)s can also be regarded as the parent structure of a series of related polymers which arc obtained not by linking the phenylene units directly, but by incorporation of other conjugated, e.g. olefinic or acetylenic, moieties. 

The ability of (Z)-l,2,4-heptatrien-6-ynes (enyne-allenes) and the benzannulated derivatives to undergo cyclization reactions under mild thermal conditions to produce biradicals has been the main focus of their chemical reactivities [1-5]. With the development of many synthetic methods for these highly conjugated allenes, a variety of biradicals are readily accessible for subsequent chemical transformations. Cyclization of the enyne-allene 1 could occur either via the C2-C7 pathway (Myers-Saito cyclization) leading to the a,3-didehydrotoluene/naphthalene biradical 2 [6-10] or via the C2-C6 pathway (Schmittel cyclization) producing the fulvene/benzofulvene biradical 3 [11] (Scheme 20.1). 

Less complex non-conjugated diene systems also lead to cubane-like derivatives as in the diene 175. Here the outcome of the reaction is dependent upon the excited state. Thus, direct irradiation brings about fragmentation with the formation of 1,4-difluorobenzene and excited-state naphthalene while triplet-sensitized irradiation follows a different path with the formation of the cage compound 17682. 

Under highly protic conditions, the major products of cathodic reductions of cyclic conjugated hydrocarbons are usually dihydro derivatives [56, 57, 187]. In 2-methoxyethanol, for example, naphthalene yields 1,4-dihydronaphthalene [187] and COT mainly provides 1,3,6,-cyclooctatriene [56, 57]. 

Table 11 shows some representative results from the cathodic reduction of some aromatic hydrocarbons. These include cases with Ei j2 near the cathodic limit or in the discharge region of the SSE (benzene, toluene) and cases with Ex j2 at considerably more positive potential (naphthalene, anthracene again we must anticipate the discussion of reactivity and refer to Table 21). Reactions nos. 1, 2, 6, and 7 immediately demonstrate one difficulty with such studies in that the catholyte of a divided cell becomes strongly basic as electrolysis progresses. In sufficiently basic medium, the initial product, a 1,4-dihydro derivative (cf. the Birch reduction Birch and Subba Rao, 1972), will rearrange to a conjugated system which, in contrast to the 1,4-dihydro derivative, is further reducible to the tetrahydro product (nos. 1 and 6). In a non-divided cell the acid production at the anode balances the base production and thus only a little rearrangement occurs. It is therefore not a trivial problem to find out if the tetrahydro product is formed from the conjugated dihydro product, formed directly or by rearrangement [eqn (78)].

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