Phenanthrene, decarboxylation

Elimination of sulfur from methyl dibenzo[/),/]thiepin-10-carboxylatcs 15 (R2 = Me) can be achieved in moderate yields (39-55%) upon refluxing in diethyl phthalate in the presence of copper bronze.60 For the dibenzo[A,/]thiepin-10-carboxylic acids 15 (R2 = H), the loss of sulfur is accompanied by decarboxylation. Thus, treatment of these acids with copper bronze in refluxing quinoline for four hours gives the corresponding phenanthrenes 16 (R3 = H) in moderate yield (50%). However, the exposure time to high temperatures influences the product formation. Thus, the decarboxyiated dibenzothiepins are obtained after refluxing for only five minutes.60... 

It has become clear that benzoate occupies a central position in the anaerobic degradation of both phenols and alkylated arenes such as toluene and xylenes, and that carboxylation, hydroxylation, and reductive dehydroxylation are important reactions for phenols that are discussed in Part 4 of this chapter. The simplest examples include alkylated benzenes, products from the carboxylation of napthalene and phenanthrene (Zhang and Young 1997), the decarboxylation of o-, m-, and p-phthalate under denitrifying conditions (Nozawa and Maruyama 1988), and the metabolism of phenols and anilines by carboxylation. Further illustrative examples include the following ... 

The biosynthesis of aristolochic acids is considered to begin with 1-ben-zyltetrahydroisoquinoline precursors and to proceed via aporphine intermediates (5). In radioactive labeling studies, Spenser and Tiwari infused d/-tyrosine-2- C into the stem of A. sipho. The C-labeled aristolochic acid I formed lost more than 60% of its radioactivity when it was decarboxylated to the corresponding nitro phenanthrene derivative. Administration of d/-dihydroxyphenylalanine-2- C re-... 

The structural determination of aristolochic acid I (1) was first accomplished by Pailer et al. Aristolochic acid I(Ci7Hn07N) is easily soluble in alkali as well as sodium bicarbonate. It was esterified with diazomethane in dioxane to give a methyl ester (C,gHi307N), and the methyl ester was readily saponified to recover aristolochic acid I. Zinc distillation of 1 gave a phenanthrene (Scheme 6). Aristolochic acid I was decarboxylated with copper powder in quinoline to yield a nitro phenanthrene derivative (OjgHjjOjN.Sl). 

The original conception of reductive decarboxylation was in terms of tin hydride chemistry, simply because of previous experience. The earlier observations,7 in the case of dihydro-phenanthrene esters, led us to think of incorporating the C=N double bond to be formed (Scheme 2) by fragmentation, into an aromatic system. This was to provide an additional driving... 

The naphthalene-2-acetonitrile (70) may serve as the source for many synthetically valuable phenanthrene-l-carbonitriles (72). The nitrile group in (72) can be converted to other functional groups or be smoothly eliminated in high yield by hydrolyzing it with potassium hydroxide in diethyleneglycole, followed by decarboxylation of the acid in boiling quinoline, in the presence of copper powder. 

One pathway to benzo(c)phenanthrene by the cyclization-elimination method has been outlined already (Section III., B. 2.) and another we will see later. A synthesis by benzannelation should start with phenanthrene-4-acetonitrile or with phenanthrene 3-acetonitrile (88) as the one component. For steric reasons the preparation of the first has only poor chances, but (88) is readily available 3-methylphenanthrene, mp. 62—63°56), obtained by hydrolysis and decarboxylation from the nitrile (72 b) (Section III., C. 3.) in an overall yield of 92% was side-chain brominated by N-bromo-succinimide in CC14, and the 3 bromomethylphenanthrene, mp. 116—117° (67%), converted to (88), mp. 82-83° (91%). 

A better chromatographic separation was achieved after hydrolysis and decarboxylation to the hydrocarbons, the 2,1 l-dimethylbenzo(c)phenanthrene, mp. 

But the sterical hindrance for angular cyclization to a dibenzo(c,g)phenanthrene is found to be so much increased here that thermolysis, achieved only under very strong conditions (240°, 12 h), leads exclusively to the linear annelated 2,11-dimethyldibenzo(b,g)phenanthrene-13-carbonitrile (99), yellow needles mp. 243— 244° (66%). Conversion of it by hydrolysis and decarboxylation gives 2,11-dimethyl-dibenzo(b,g)phenanthrene, mp. 155—156°. 

Pure benz(c)phenanthrene, mp. 67—68° and 2,1 l-dimethylbenz(c)phenanthrene, mp. 129—130°, can be simply obtained hydrolyzing 148a) or 148 b) by potassium hydroxide in triglycol at 180° and decarboxylation of the dicarboxylic acids in boiling quinoline in the presence of copper powder, giving a 91% or 70% yield, respectively32 The sterically screened carbonitrile groups in 148 d) and 148 e) cannot be saponified. 

Nitroveratric aldehyde and 3 4-dimethoxyphenylacetic acid were condensed to give the acid [xv, R = H]. Reduction and Pschorr phenanthrene ring-closure of this gave two tetramethoxyphenanthrene carboxylic acids one of these, also accessible from the bromo-acid [iv, R = Br], must be the 3 4 5 6-isomer [v] and the other the 3 4 6 7-isomer [yi]. The latter on decarboxylation afforded dimethylsinomenol [u, R = Me]. 

Addition Reactions.- The photoelectron transfer process of the iminium salt (38) with the 3-butenoate anion results in the formation of the allylated product (39). The reaction involves decarboxylation of the 3-butenoate followed by a radical coupling reaction. The photoaddition of halogenated alkenes to the tetraraza phenanthrene (40) yields products (41) of (2+2)-addition. The Eu(III)/Eu(II) photoredox system has been studied with regards to its reactivity toweu ds a-methylstyrene. Irradiation of the system at > 280 nm in methanol yielded the products (42) and(43). ... 

Substituted phenanthrenecarboxylic acids can be obtained in this way and yield the phenanthrene hydrocarbons on decarboxylation. Weisbach and his co-workers803 applied this reaction to synthesis of aporphine. 

Crebanine, C20H21O4N, present in S. sasakii (44) and in S. capitata (45) melts at 126°. It is non-phenolic and upon oxidation by permanganate afforded hemipinic acid. It was submitted to Hofmann degradation, the nitrogen-free compound oxidized, and the latter utimately decarboxylated to yield a phenanthrene derivative (m.p. 111-112°) which was stated to be identical with a synthetic specimen of l,2-dimethoxy-5,6-methylene di-oxyphenanthrene (46, 47). In view of these observations crebanine must be XXI in which the methoxyls are in positions not accountable for by... 

The AT-methylanonaine was obtainable by reaction with forniic acid and formaldehyde, and Hofmann degradation via A-methylanonaine methiodide (m.p. 217°) gave a methine base (m.p. 87-90°) and a vinyl-phenanthrene (m.p. 87°) which on oxidation generated a phenanthrene-carboxylic acid (m.p. 240°) which could be decarboxylated to what was evidently 3,4-methylenedioxyphenanthrene (m.p. of picrate, 168°). 

Several radical intermediate-based methodologies have been introduced for decarboxylations as an extension of earlier efforts on the deoxygenation of alcohols. One of the early approaches involved the TBTH reduction of the dihydrophenanthrene derivative of carboxylic acids (equation 71). However, the difficulties associated with the preparation of the phenanthrene ester derivatives and lack of success with tertiary carboxylic acids proved to be disadvantageous. A more notable discovery in this context is the demonstration that esters derived from COOH groups attached to primary, secondary and tertiary carbons and iV-hydroxypyridine-2-thione undergo efficient reductive decarboxylation in the presence of TBTH in refluxing benzene or toluene... 

Application of this technique to the identification of methyl esters of the organic acids obtained by the controlled oxidation of bituminous coal allowed the more volatile benzene carboxylic acid esters to be identified (Studier et al., 1978). These were esters of benzene tetracarboxylic acid, tere-phthalic acid, toluic acid, and benzoic acid. Decarboxylation of the total acid mixture was shown to afford benzene, toluene, Cj-benzenes (i.e., ethylbenzene or xylenes), Cj-benzenes, butylbenzenes, Cj-benzenes, Cybenzenes, naphthalene, methylnaphthalene, C2-naphthalene, biphenyl, methylbi-phenyl, C3-biphenyl, indane, methylindane, Cj-indane, phenanthrene, and fluorene. 

Decarboxylation of A -Boc-L-valine has been performed in polar solvents, using electron acceptors such as dicyanobenzenes, methyl 4-cyanobenzoate, and 1,4-dicyanonaphthalene as photosensitizers, in combination with several arenes (phenanthrene, naphthalene, 1-methylnaphthalene, biphenyl, triphe-nylene, and chrysene) as co-sensitizers. The best result is achieved using biphenyl and 1,4-dicyanonaphthalene in aqueous acetonitrile. This type of reaction has been applied to the photodecarboxylation of A -Boc protected amino acids and other free carboxylic acids, in the presence of thiol and a small amount of D2O, to obtain products with high deuterium content. 

SCHEME 22.23 Synthesis of phenanthrenes by Pd-catalyzed decarboxylative coupling of 2-phenylbenzoic acids with alkynes. 

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