Bibenzyl derivatives

Fig. 12 Variation of the rate constant with the driving force in the homolytic cleavage of various types of anion and cation radicals. The open symbols refer to bibenzyl derivatives and the stars to cation radicals of the tm-butyl derivatives of synthetic analogs of NADH.

Studies on phytotoxicity of bibenzyl derivatives were extended to duckweed axenic cultures. Bibenzyls 19 and 20 as well as the synthetic analogs 23—28 were tested by triplicate in cultures of the small aquatic plant. Analogs 23—28 were synthesized to investigate the effect on phytotoxicity of oxygenated substituents (phenolic vs. phenolic methyl ether) and their location on the bibenzyl core structure. All synthesized analogs but... 

Table 1. Effect of Bibenzyls 19,20,23-28 on Duckweed Cultures at 72 Hours. (Reprinted from J Agric Food Chem, 53, Hernandez-Romero Y, Acevedo L, Sanchez MD, Shier WT, Abbas HK and Mata R, Phytotoxic activity of bibenzyl derivatives from the orchid Epidendrum rigidum, 2005, 6276-6280 with permission from ACS.)...

The phase-transfer method has also been employed for the carbonylation of benzylic halides to carboxylic acids.477 The palladium(O) complexes [Pd(PPh3)4] (103), [Pd(diphos)2] (104) and [Pd(DBA)2] (105 DBA = dibenzylideneacetone) were used as catalysts. With (103) and (104) the carboxylic acid was the major product. Complex (105) gave little or none of the acid, the toluene and bibenzyl derivatives corresponding to the benzyl halide used being formed. Benzyl esters of the carboxylic acid were sometimes present as minor products. The reaction has been adapted to provide a new synthesis of anthranilic acid derivatives (equation 106).478 Tri-n-butylamine was used to neutralize the HBr formed. 

Similar results from product studies were observed with toluene as the substrate (Ross et al., 1970). Voltammetric curves from substrates with relatively high oxidation potentials were in all cases markedly displaced towards higher potentials upon addition of the toluene, a phenomenon ascribed to blocking of anode sites by adsorption of toluene. Hexamethylbenzene, with Ex j2 considerably lower than the discharge potential of nitrate ion, gives a mixture of the a-nitrate and acetate upon oxidation at 1 1 V versus see, demonstrating at least in this case that these can be products of a direct oxidation mechanism. In all cases small amounts of bibenzyl derivatives were formed, which of course necessitates the intervention of benzyl—but not nitrate—radicals at some stage of the mechanism. 

In the course of the electrochemical conversion, the bibenzylic intermediate 4 is then further converted into the desired products 2 and 3 by cleavage of the central C,C-bond (Fig. 5.3) (Zollinger et al. 2004b). C,C-bond cleavages of stilbene or bibenzyl derivatives are observed at graphite electrodes only at elevated current densities (10 A dm-2). 

The C-C bond cleavage in photogenerated radical cations of bibenzyl derivatives is probably the most studied fragmentation process [102, 103, 107, 112-115] among various PET systems (Scheme 4). The benzene, toluene or... 

Carbon-carbon cleavage has been extensively investigated. Thus bibenzyl derivatives when irradiated in the presence of 1,4-DCB and methanol form the... 

Majumder PL, Guha S, Sen S (1999) Bibenzyl Derivatives from the Orchid Dendrobium amoenum. Phytochemistry 52 1365... 

Evidence has been obtained that the photodecarboxylation of benzannelated acetic acids in aqueous solution proceeds via carbanion intermediates 5H-dibenzo[a,d]cyclohepten-5-carboxyl-ic acid, for example, undergoes photodecarboxylation with a quantum efficiency of close to unity. The reactions of the -nitrobenzyl anion, generated by photochemically induced loss of carbon dioxide from -nitrophenylacetate anion, have been examined and a mechanism proposed to account for the formation of the corresponding bibenzyl derivative. Reductive decarboxylation of carboxylic... 

Reduction of o- and / -nitrobenzyl halides at mercury or platinum gives mainly the bibenzyl derivative, with nitrotoluene as a minor product [121-126]. However, m-nitro-toluene is the predominant product of the electrolysis of / -nitrobenzyl halides [123]. 

The ethane bridge of compound 167 from the roots of Deguelia hatschbachii A. M. G. Azevedo was oxygenated to be a keto [47]. Racemosol and demethylracemosol, together with their possible biogenetic precursors, preracemosols A and B (175, 176), were isolated from the roots of Bauhinia malabarica Roxb, in which methylation occurred at C-4 position [101]. From Radula laxiramea, twelve bibenzyl derivatives and the common bisbibenzyl perrottetin E were isolated. 

Boekelheide and Phillips815 achieved the synthesis of the interesting /ra/ .r-15,16-dimethyldihydropyrene (17) and found that by all criteria, including both spectral properties and chemical reactivity, this hydrocarbon having substituents within the cavity of the (4n + 2) electron cloud is an aromatic molecule. In their synthesis, indicated briefly in the formulation, one meta link between two molecules of (8) is established by reaction with magnesium in the presence of ferric chloride to produce the bibenzyl derivative (9). Reaction of the diiodide (14) with finely divided sodium and tetraphenylethylene in tetrahydrofurane establishes the second meta link... 

Bryophytes, constituents of (constituents of mosses). Bryophytes produce numerous secondary metabolites that have not yet been found in other plants. They are mostly phenolic compounds and terpenes, there are considerable differences between the individual classes of mosses. Homworts (Anthocerotae) are characterized by the presence of lignans, liverworts (Hepaticae) principally by terpenes, especially sesqulterpenes that are often enantiomers of the compounds found in higher plants and bibenzyl derivatives. Mosses (Musci) contain biflavonoids (see flavonoids), sphagnorubins (peat mosses) and cou-marin derivatives. Alkaloids are rare and have as yet only been found in liverworts. 

Tyrolobibenzyls are a new class of naturally occurring bibenzyl derivatives possessing a unique phenylethyl-benzofuran skeleton. Tyrolobibenzyls A 119,... 

Majumder PL, Roychowdhury M, Chakraborty S (1997) Bibenzyl derivatives from the orchid Bulbophyllum protractum. Phytochemistry 44 167-172... 

Kraut L, Mues R, Zinsmeister HD (1997) Prenylated bibenzyl derivatives from Lethocolea glossophylla dmdRadula voluta. Phytochemistry 45 1249-1255... 

Oiso Y, Toyota M, Asakawa Y (1999) Occurrence of a bis-bibenzyl derivative in the Japanese fern Hymenophyllum barbatum first isolation and identification of Perrottetin H fiom the Pteridophytes. Chem Pharm Bull 47 297-298... 

Twenty-five Frullania species were investigated chemically bibenzyls derivatives (595—597, 600—608) were detected in twelve species and five species contained methylenedioxy bibenzyls as shown in Table I (27). 

In Frullania, twenty-five taxa have been investigated chemically (27,34). Fourteen species contained allergy-inducing sesquiterpene lactones such as (322, 338, 339, 345, 349). Eighteen species bibenzyl derivatives (595—598, 600—608). The major constituents are sesquiterpene lactones and bibenzyls, which may be valuable chemosystematic markers of Frullania species. Frullania species are divided into five chemotypes, a sesquiterpene lactone-bibenzyl type (Type I), a sesquiterpene lactone-type (Type II), a bibenzyl-type (Type III), a monoterpene-type (Type IV) and a cyclocolorenone (38)-type (Type V). Except for the cyclocolenone-type, there is no chemical affinity between the Frullaniaceae and the Porellaceae. 

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