Senecio aldehyde

Reactions with 3-methylbutanal (82) (for ipsenol, 83) or senecio aldehyde (dimethylacrolein, 84, for ipsdienol, 85) were discussed previously (Vol. 4, p. 467). Many further publications on the subject have s peared. Isoprene can be tribrominated, first with bromine in carbon tetrachloride, then with N-bromosuccinimide. This is one route to 2-bromomethyl-l,3-butadiene (9, R = Br), obtained from the tribromide with zinc amalgam reduction, but in fact the tribromide reacted directly with the aldehydes 82 or 84 to give ipsenol (83) or ipsdienol (85). A reagent used for the reaction of 9 (R = Br) with the aldehydes... 

The establishment of natural artemisia alcohol from sage as the (5)-isomer was announced by Zydowsky and Hill in 1982, and an elegant synthesis of both enantiomers by H.C. Brown utilizes the chiral borane 219, which contains a prenyl group. Reaction of the illustrated enantiomer with senecio aldehyde (84) gave the addition product from which (- )-(S)-artemisia alcohol [(- )-209] was obtained after alkaline peroxide oxidation in 96% ee. ... 

The structure of benulin (134), a lupene hemiacetal from Bursera arida, has been confirmed by X-ray analysis. An investigation of several Senecio species has resulted in the isolation of a series of lupane derivatives which include the acids (135), (137), and (139), the corresponding aldehydes (136), (138), and (140), the ketone (141), and betulonic acid. Three more triterpenoids (142)—(144) have... 

In the first reports on the use of esters of 4-bromo-2-butenoic acid (191a and b, crotonic acid) and of 4-bromo-3-methyl-2-butenoic acid (191c, senecioic acid), the corresponding Reformatsky reactions with benzaldehyde were performed with the old-fashioned procedure, which required heating the haloester, the aldehyde and granulated zinc in benzene/ether mixtures at reflux temperature. 

Senampelines C (37) and D (38) have again been isolated, as a mixture, from Senecio mikanoides [Otto ex] Harv. ° In addition, three new senampelines, i.e. E (39), F (40), and G (41), were also present in this species, in the ratio 2 1 1. The structures of senampelines E—G were determined by H n.m.r. spectroscopy and by degradation by methoxide to the corresponding aldehyde esters (42). °... 

A general procedure has been published for the synthesis of retinoids, including vitamin A, by direct condensation of the side-chain, as ethyl 3,7-dimethylnona-2,4,6-trien-8-ynoate (80) to the appropriate cyclic ketone, e.g. 2,2,6-trimethyl-cyclohexanone (81). The acetylenic intermediate (82) is readily converted into vitamin A and derivatives. The side-chain reagent (80) is prepared in high yield by Emmons reaction between the acetylenic aldehyde (83) and the phospho-senecioate (84). In another synthesis of trans- tamm A, jS-ionylideneacetal-... 

Aldol condensation of the retro Cj5 aldehyde (284) with ethyl senecioate (285) in the presence of potassium amide gave 4,6-retroretinoic acid (286). This compound reacted with methyl iodide to give the methyl ester, which was reduced with lithium aluminum hydride to 4,6-retroretinol (287) ( a-vitamin A ). Treatment of (287) with triphenylphosphine hydrochloride gave the C20 phos-phonium salt (288), while oxidation of (287) with manganese(IV) oxide produced the aldehyde (282) (Isler, 1971). 

A number of converging syntheses of 3,4-didehydroretinoids employed the same strategies that have been successfully employed for the synthesis of the natural retinoids (1), (2), and (3). Alkali-catalyzed condensation of the dehydrogenated C 5 aldehyde (294) with ethyl senecioate (285) gave, after esterification, ether (295) or (296), which were converted to the alcohols (289) or (297), and to the aldehydes (290) or (298) (Schwieter et aL, 1962b). 

The Ci5 aldehyde (4) condensed with ethyl senecioate (285) in the presence of sodium amide or lithium amide to give (13Z)-retinoic acid (17), which was converted to the methyl ester and then reduced to give (13Z)-retinol (346). Oxidation of the latter gave (13Z)-retinaldehyde (41) (Matsui et aL, 1958). 

When, however, the chain-lengthening reactions with the pure Cj5 aldehyde isomers (349) and (350) were carried out using methyl 4-diethylphosphono-senecioate ( /Z = 1.3), conventional secondary reactions gave mixtures of the aldehydes (354) and (356) and of the aldehydes (355) and (356), and these mixtures were separated by chromatography (Asato and Liu, 1975 Ramamurthy and Liu, 1975 Ramamurthy et aL, 1975 Liu and Asato, 1982). ... 

Condensation of the Cj5 aldehyde (347) with ethyl senecioate (285) in liquid ammonia or anhydrous ether in the presence of potassium amide gave (9Z)-retinoic acid (348), which was methylated in a conventional manner with diazomethane to give methyl (9Z)-retinoate (357). Reduction of (357) with lithium aluminum hydride gave (9Z)-retinol (132), which was oxidized with man-... 

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