Alkenylphenols

Very long chain n-alkenylphenols (60) accounting for ca 1.5% of dry biomass were identified in the external lipids of the collection strain from Austin (56) and detected in all the strains of the A race examined so far. Isolated by TLC as a solid mixture, these compounds exhibit an UV absorption maximum at 215 nm (e7500) and IR bands at 1600 and 3560 cm both indicative of a phenol moiety. 

A polyketide origin for (60) was established by feeding experiments with sodium [1,2- C] acetate (Fig. 13). According to the coupling 

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Although l,2-methylenedioxy-4-allylbenzene and 1,2-methylenedioxy-4-prope-nylbenzene are really heterocyclic compounds, they are discussed here because of their close biogenetic relationship to the 2-methoxy-4-alkenylphenols. 

Pathway G Synthesis of 2-(l-hydroxyalkyl)benzofuran derivatives from o-alkenylphenols. o-Allylphenols and their benzyl ethers (168), treated with a peroxy acid, give epoxides which, according to conditions, lead... 

The double dehydrogenation of o-alkylphenols to chromenes has also been achieved with DDQ, the reaction presumably proceeding through the alkenylphenol rather than the chroman. The latter are not known for their propensity to undergo oxidation by DDQ unless a free hydroxyl group is present to allow quinone methide formation to occur. Once again, substitution at C-3 appears to be essential for success. 

The cyclisation of o-alkenylphenols features in two approaches to the chroman ring system. The Hg-mediated cyclisation of (7) affords the chroman-4-ols (8) and (9) which can be separated after debenzylation, providing the chroman unit of the calophyllum coumarins (95S630). 2-Cyclohexenylphenols undergo a 6-endo cyclisation to fused chromans on treatment with pyridine hydrobromide perbromide (95CJC1727). 

A similar concept based on a mixture of BMI-MDA (Matrimide 5292 A) and bis-alkenylphenol (Matrimide 5292 B) with a flexible polyimide has been patented as a heat-resistant adhesive [117]. 

One simple way for arriving at a photoinduced Markovnikov-type amination of olefins is illustrated in Scheme 3.15, for the case of o-alkenylphenols (e.g., 24). Here, an ammonium salt of the o-alkenylphenolate anion (25) is prepared and irradiated this causes proton transfer within the ion pair (from the amine to the olefin), and the resulting zwitterion undergoes nucleophilic addition of the amine at the benzylic cation center. The addition is selective for N- rather than O-nucleophiles, as shown in the case of ethanolamine [34]. 

Yasuda, M., Sone, T., Tanabe, K., and Shima, K. (1994) Animation of o-alkenylphenols via photoinduced proton transfer. Chemistry Letters, 453-456. 

The amination of 2-alkenylphenols occurred efficiently compared to 2-allylphenols and -naph-thols69. The mechanism involves a proton exchange equilibrium between the phenolic and amino functions and the photoinduced proton transfer (PPT) from the ammonium ion to the alkenyl group, followed by attack of the amine on the intermediate benzylic carbocation. No photoamination of O-methylated and O-acetylated phenols occurred at all. As a single example of diastereoselective amination, the amine 6 was produced from 5 with good yield and diastereoselectivity, although the configuration was not determined. 

Pyrolysis also has been utilized for the determination of the structure of unique natural polymers in certain lacquers such as those produced by Rhus vernicifera and Rhus succedanea [2] and utilized as surface coating for wood, porcelain, etc. in Japan. The pyrolysis products of the two lacquer films at 400° C contain respectively laccol and urushiol, and each also contains alkenes, alkanes, alkenylphenols, and alkylphenols. From these results it was possible to assign the following structure for laccol polymer ... 

The quinone methides 343 undergo a rapid and practically quantitative rearrangement on neutral alumina at 70-80 °C to afford the alkenylphenols 344 (equation 164). 

A number of bicyclic and polycyclic phenols have been prepared invariably from cycloaliphatic intermediates and these have been classified in this section which essentially describes alkenylphenol derivatives. 

The possibility of the occurrence of unusual condensation reactions with alkylphenols might be anticipated from the increased activation of the ring. Amongst the first, dimerisation of the alkenylphenol shown may be mentioned. 4-iso-Propenylphenol intrifluoracetic acid at ambient temperature furnished after 5mins.,1-(4-hydroxyphenyl)-1,3,3-trimethylindan-6-olin acceptable yiekJ(ref.64). 

In recent years considerable attention has been given to the biodegradability of polyethoxylates and the role of their structure in this process. In consequence, there has been a move away from multi-branched alkyl side-chain in the starting alkylphenolic raw material towards more linear chains, a circumstance already adopted in the use of kerylbenzenes for the manufacture of alkylaryl sulphonates. Another practice adopted has been that of sulphation of the terminal hydroxyl group in the polyalkoxylate. Recent studies on a comparison of ethoxylates derived from the natural alkenylphenol, cardanol and from nonylphenol have indicated a considerable difference in biodegradability (ref. 24). 

Several of the alkenylphenols referred to in the series discussed were found to possess interesting perfumery odours. 

The reactions of the alkenylphenols resulting in the syntheses referred to have been studied v h respect to the derivation of methylol compounds and the formation of unsaturated ethers. 

The reaction of phenol with natural C q (and C.,5) acyclic hydrocarbons such as the readily available myrcene, ocimene or alloocimene from the replenishable source pine oil, does not seem to have been examined in detail although the semi-synthetic 4- and 2-alkenylphenolic products obtained from it could be... 

Under severe acid-catalysed reactions of isoprene with phenols, chromans always accompanied the 2- and 4-alkenylphenols (ref. 2). 

Some of this group are listed in Table 13.3 All the members are 3-alkenylphenols sometimes, as with campnospermanol, containing a keto function in the side chain. The highly unsaturated substance flexirubin is a phenolic ester from a bacterial source. Complex phenolic ether compounds, essentially 0-glycosyl derivatives of c6-(4-hydroxyphenyl)phthiocerol A have been isolated from mycobacterial sources (ref. 75). 

Yasuda et al. have recently reported that irradiation of o-alkenylphenols and naphthols in the presence of primary or secondary amines results in Markovnikov addition of the amine. For example, irradiation of the alkenylphenol 12 with methyl-amine affords the adduct 13 (Scheme 4), The initial step in these reactions is proton transfer from the acidic phenol singlet state to the amine, which leads to the formation of the singlet phenolate anion and ammonium ion. Proton transfer from the ammonium ion to the phenolate anion yields a zwitterion, which undergoes nucleophilic addition of the amine. Thus the amine serves as a base in the initial step of this reaction and then as a nucleophile. 

Alkenylphenols underwent Pd(OAc)2-PPh3 catalyzed regioselective hydroesterification with phenyl formate as CO source to afford five- and... 

Hydroxysilyl groups can also act as directing groups in the alkenylation. As the substituents are removable, the sequence of alkenylation/desilylation of silanol substrates leads to the (semi-) one-pot syntheses of 2-alkenylphenol [26] and 2-alkenyltoluene derivatives [27] (Scheme 18.26 and Scheme 18.27). 

Diverse dihydronaphtho[l,2-(r]furans were generated fix)m 1,4-naphthoquinones and olefins in the presence of ceric ammonium nitrate (13OBC6097). ( )-Lantalucratins A and B were produced in the presence of diammonium cerium(IV) nitrate (13T10470).Benzo[(>]furan moieties were synthesized by a three-component Mannich reaction of 3-acetyl-2H-chromen-2-one or l-(l-benzo[fc]fioran-2-yl) ethanone with p-substituted aromatic aldehydes and aromatic amines with ceric ammonium nitrate (CAN) as a catalyst (13MCR4787).p-Alkenylphenols went through the oxidative dimerization to generate substituted dihydrobenzo[l)]furans in the presence of CAN (13T653). 

Note here that, as shown in Scheme 9, the methyl carbon of 2-butenyl or 2-pentenyl moiety of the starting 2-alkenylphenols can be functionalized via the resulting 2-vinyl-2,3-dihydrobenzofuran or 2-vinylchroman with nucleophiles in the presence of palladium(O) catalyst. ... 

Bismaleimides may also be treated with hydroxylamine/ dicarboxylic acids/ " aminophenols/ alkenylphenols/ " phenolics with two or more OH residues/ triazene resins/ hydrogen sulfide, bisthiols or polythiols, organocyanates, such as 2,2-bis(4-... 

Bisisomaleimide, hexamethylene, rearrangement to bisimide, 89 Bismaleimides aliphatic, crosslinked, 511 alkenylphenols condensation, 514 aromatic cycloaddition reactions, 266 azomethine condensations, 515 condensation polymer modifiers, 511 crosslinking monomers, 91 crotonitrile condensations, 515 dialdoximes condensation, 514... 

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