Ethylidene Groups

One result of all these reactions is the change of the vinyl group to an ethylidene group (CHj CH. -A-CH3. CH ) with the formation of the opo-bases, e.g., opocinchonidine and 3-cinchonidine, which are the two geometrical isomerides required by the formula (E Q = quinolyl residue). 

Another transformation observed with a naturally occurring bacteriochlorin is the tautomer-ization of the exocyclic C — C double bond in bacleriochlorophyll b (3) in acetone which gives 7,8-dehydrobacteriochlorophyll a (4), a chlorin-type product (configurations at C7 and of the 8-ethylidene group have not been established).112,12... 

The isolation of isoantirhine, having a side chain containing an ethylidene group, and methoxyantirhine, having a methoxy substituent on ring A, has also been reported (23, 24)-, however, no physical or spectroscopic data are available. 

Stereoselective allylic alkylations have been carried out with the aid of palladium catalysts. The 17-(Z)-ethylidene groups of steroids (obtained from the ketones by Wittig olefination) form n-allyl palladium complexes in the presence of copper(n) salts (B.M. Trost, 1974, 1976). Their alkylation with dimethyl malonate anions in the presence of 1,2-ethane-diylbis[diphenylphosphine] (— diphos) gives a reaction exclusively at the side chain and only the (20S) products. If one starts with the endocyclic 16,17 double bond and replaces an (S)-20-acetoxy group by using tetrakis(triphenylphospbine)palladium,the substitution occurs with complete retention of configuration, resulting from two complete inversions (B.M. Trost, 1976). 

An interesting follow-up was a variation of the first reaction in which the methylene group of compound 174 was replaced by a as- or /raar-ethylidene group, which led to one or the other of the two diastereomers 177 and 179,... 

Two papers have thrown light on the finer structure of Appel s diacetal. First, Gatzi and Reichstein141 oxidized it with potassium permanganate in alkaline solution and obtained a diethylidene-L-xylonic acid, together with a monoethylidene-L-threonic acid. The ethylidene group in the latter compound was shown to span positions 2 and 4, from which they concluded that the parent diacetal was 1,3 -diethylidene-D-sorbitol (XXXI). Secondly, Bourne and Wiggins117 hydrolyzed the... 

The structural data from which the structure of vinoxine (89) was deduced have been described in greater detail.65 The configuration at C-16 is based on the closer resemblance of the XH n.m.r. spectrum of vinoxine to that of 16-epipleiocarpamine rather than that of pleiocarpamine. In reference 65, for some unspecified reason, the configuration given for the double bond is different from that illustrated in (89) and postulated in the earlier communication 334 however, the similarity of the chemical shifts of the protons of the ethylidene group with the corresponding ones in the pleiocarpamine series makes it extremely probable that the configuration about the double bond [i.e. (Ij)] is the same in all these alkaloids. 

The presence of an allylamine system in pseudoakuammigine, postulated in XLVIII, is confirmed by the platinum-catalyzed hydrogenolysis of pseudoakuammigine methiodide, which affords a dihydromethine base, C23H30N2O3, by fission of the C-21 to Nb bond the apo base methiodide similarly yields a dihydromethine. Both bases still contain the ethylidene group, and contain one additional C -methyl group. 

The presence of an ethylidene group in echitamine chloride was also demonstrated by oxidation with periodic acid, which was reported to give acetaldehyde and indole-3-acetaldehyde (78). Alkali fusion and selenium dehydrogenation experiments gave inconclusive results, but the basic fractions were suspected to contain derivatives of jS-carboline (77, 78). Oxidation of echitamine with alkaline potassium permanganate afforded a low-melting base, which was considered to be Nb-methyl-tryptamine (80). 

Huntrabrine methochloride has an ethylidene group, a quaternary IV-methyl, a 5-hydroxyindole chromophore, and a primary hydroxyl group. It underwent a facile Emde degradation, and the resulting tertiary base upon tosylation gave a phenolic-O-tosylate quaternary tosylate. The latter compound, upon selenium dehydrogenation, afforded uncharacterized products, one with a sempervirine-like UV-spectrum and another with a 2-pyridylindole chromophore. All these results are interpreted as supporting the structure XLVI (see Table I) for huntrabrine methochloride (27). 

NMR-absorption at 8.72 8 (Na-H) and 3.78 8 (CO2C//3). NMR-spectro-scopy also showed that the ethylidene group of stemmadenine was still present. The absorption in the 4.0 8 region (which may be assigned to protons allylic to one double bond and next to nitrogen, or to protons allylic to two double bonds) showed two single proton absorptions. Position 3 (partial structure CCXIX) is therefore substituted and can only be linked to C-7, while C-16 may be linked to positions 15 or 21... 

A determination of the structure of akuammidine by X-ray analysis (75) provides a second starting point for the collection of a set of interrelated structures having the same configuration at the ethylidene group again, one must make use of the various chemical correlations already outlined in the chapter. 

Ozonolysis has been of value in determining the presence or absence of ethylidene groups (197). 

Geissoschizine (XII), C21H24O3N2 (mp 194°-196°, [a]D+ 115°), is the second cleavage product when geissospermine is treated with hydrochloric acid (3). It is amphoteric and has one O-methyl and two active hydrogens and its IR-spectrum shows the presence of C=0, NH, and OH groups. The presence of an ethylidene group was demonstrated by... 

The stereochemistry of the ethylidene group could not be decided from these experiments but it came from the results of the X-ray work carried out on the correlated compounds (Chart IV), macusine A (28) and akuammidine (27). 

A decrease in the initial band at 807 cm-1, attributed to the ethylidene group of the norbomene moieties, was measured. The total disappearance of this band at 807 cm-1 was obtained after about 20 h of irradiation. During the same period, the absorbance at 3450 cm-1 due to the formation of hydroperoxides increased rapidly. Taking into account an absorption coefficient e socm- ) of 75 kg/mol cm and an absorbance AOD (change in optical density) = 0.17, the concentration of ROOH was estimated to 0.23 mol/kg. This concentration of hydroperoxides formed during the first 20 h of irradiation was close to the concentration of the ethylidene groups. 

The application of carbenoid reactions, however, gives satisfactory results in certain cases. Thus, ethylidene iodide with diethylzinc transfers an ethylidene group to olefinic double bonds in good yields ". The reaction proceeds in a stereospecific manner (equation 50). Stereochemical control of the addition by hydroxyl groups similar to those... 

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