Bisabolene synthesis

This is the synthesis carried out by Vig and his group. (J. Indian Chem. Soc.. 1966, 43, 27). Bisabolene has been made in several other ways. 

The stereoselective synthesis of y-bisabolenes was made possible by the development of a new method for the carbosilylation and double alkylation of an acetylenic function coupled with ring closure, overall addition of three carbon substituents to two acetylenic carbons. 

The acetylenic alcohol A, which was used as a key intermediate in the synthesis of ( )-7-bisabolene, served as the starting point of this synthesis. 

Both E- and Z-isomers of the terpene y-bisabolene have been isolated from natural sources. The synthesis of these compounds can be achieved by stereoselective alkene syntheses using borane intermediates. An outline of each synthesis is given below. Indicate the reaction conditions that would permit the stereoselective synthesis of each isomer. 

In the synthesis of the monocyclic bisabolene-type sesquiterpenoids (-f)-curcuquinone and (—)-curcuhydro-quinone, 1,3-diol 107 was obtained by ozonolysis of 4,5-dihydro-l,3-dioxepin 106 (obtained by Heck reaction, see Section 13.11.10) and reductive workup (Scheme 25) <2003ARK232>. 

The reagent (2) has been used for a total synthesis of paniculide A (4), a highly oxygenated bisabolene, by annelation of methyl a-formylpropionate with 2 followed by dehydration.2... 

This selective metalation has been used for the synthesis of several bisabolane sesquiterpenes. Thus the sesquiterpene (- )-J -bisabolene (7) can be synthesized in one step from metalated ( —)-limonene by reaction with I-bromo-3-methyl-2-butene. Two... 

Vig et al. have reported the syntheses of y-bisabolene (59) and dehydro-a-curcumene (60). Both isomeric atlantones (61) and (62) have been isolated from Cedrus deodara and a-bisabolol (63) has been isolated from the essential oil of the cotton plant. Two syntheses of nuciferal (64) have been reported by Cast and Naves starting from 2-(p-tolyl)propanal. Russian workers have described the synthesis of Ar-juvabione (67) by alkylation of the )8-keto-ester (65) with (66) followed by hydrolysis, decarboxylation and re-esterification. The isolation and... 

Characterization of (JE )-y-bisabolene (55a) has recently been accomplished for the first time by its synthesis from a jS-hydroxy-acid (53a) whose absolute configuration was established by X-ray crystallographic analysis. The g.l.c. and spectral characteristics of (Z)-y-bisabolene (55 b), produced from the diastereomeric acid (53b), were also recorded.Thus it can be concluded that the previous synthetic route to y-bisabolene (Vol. 6, p. 57) produced a 3 2 ratio of E) and (Z)-isomers. As a result of these definitive studies the proper identification of y-bisabolene in natural systems can now be made. 

A low yield synthesis of p-bisabolene (104) has been achieved by reaction of ( +)-limonene with acetic acid and acetic anhydride in the presence of manganese (III) acetate to give the acid (105) which could be converted into p-bisabolene in... 

Molecules like bisabolene with several alternative first disconnections are typical cases where it is helpful to consider convergence. The fungal metabolite trisporic acid (15) is a more testing example. The two central double bonds (a) and (b) offer possible Wittig disconnections. The less central (b) leads to an easily synthesised halide (17) (Chapter 25) and a difficult ketone (16), but the more central (a) leads to two nearly equal fragments (18) and (19) and to a more convergent synthesis. 

Owens, T.D., Souers, A.J. and Ellman, J.A. (2003) The preparation and utility of bis(sulfinyl) imidoamidine ligands for the copper-catalysed Diels-Alder reaction. The Journal of Organic Chemistry, 68, 3-10 Kochi, T. and Ellman, J.A. (2004) Asymmetric a-alkylation of N -tert-butanesulfinyl amidines. Application to the total synthesis of (6R,75)-7-amino-7,8-dihydro-a-bisabolene. Journal of the American Chemical Society, 126, 15652-15653. 

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