Diterpene chemistry. II. The preferential oxidation of the vinyl groups of pimaric and sandaracopimaric acids

Abstract

The use of the Lemieux -von Rudloff technique for the oxidation of the vinyl groups of pimaric (Ib) and sandaracopimaric (IIb) acid methyl esters has been investigated. Although the process leads to the expected C-13 acid V in the case of methyl sandaracopimarate, an unexpected epoxy acid was obtained from methyl pimarate. This product was shown to be the 8p,14p-epoxy-13-a-ketoacid V I I I a , probably arising from an intramolecular process during oxidation of the vinyl group.Canadian Journal of Chemistry. Volume 45, 1439Volume 45, (1967 Our interest in diterpene resin acids of the pimaric acid type (Ia, IIa) led us to consider these compounds as starting materials for the partial synthesis of other natural products; for instance, novel steroidal derivatives should be available by the formal insertion of one carbon atom, as illustrated in 111. The nuclear double bond between C-8 and C-14 and the vinyl group a t C-13 represent positions for elaboration of functions for carrying out such transformations (1). Accordingly, we studied the conversion of these groups into those more useful for ring closure.T o achieve a stepwise synthesis, different functionality was required a t the double bonds mentioned. The enhanced reactivity of the vinyl group to hydrogenation (2, 4), hydroboration (3), and hydroxylation (4) suggested that a preferential oxidation process should be possible a t that site, leading to acids of type IV. A sequence paralleling that of Edwards (4) or a similar method (5) would seem possible, but in our hands this route proved impractical since relatively large amounts of the C-13 acid could not be obtained in a high yield or in a sufficiently pure form for further studies. I t was thus decided to attempt a selective oxidation of the vinyl group; the method vie considered most amenable to variations in the reaction parameters was that of Lemieux and von Rudloff (6). This tech-niclue involves the use of a c a t a l~~t i c amount of potassium permanganate in a buffered solution of sodium metaperiodate. The double bond is attacked by the permanganate, which is continually being regenerated from its reduced state by the periodate. Any glycols or a-ketols (8-9) that are formed are then cleaved by the excess periodate present ; further oxidation of aldehydes by permanganate to acids ensues. This method was applied to the methyl esters of pimaric (Ib) and sandaracopimaric acids (IIb), and the results are described in this r e~o r t .T h e oxidation of methyl sandaracopimarate (IIb), using 4 M equivalents of periodate with t-butyl alcohol as solvent (lo), gave 55% of the ester acid V, whereas 6 equivalents of oxidant gave 85% of this product, whose structure was deduced as follows. T h e infrared spectrum showed absorption characteristic of an acid (3 100 and 1 695 cm-l) and an ester (1 735 cm-l), and the nuclear magnetic resonance (n.m.r.) spectrum showed a single unsplit peak in the olefinic region a t 4.43 T, indicating loss of the vinyl group. T h e methyl signal attributable to the C-13 methyl group (11...

Cyclo‐depolymerisation of polyundecanoate and related polyesters: characterisation of cyclic oligoundecanoates and related cyclic oligoesters

“…10-Bromodecanoic acid was prepared by oxidising the commercially available 11-bromoundec-1-ene with sodium periodate and a catalytic amount of potassium permanganate. 44 The molecular weights of the linear polymers are given in the Experimental section. These linear polymers were cyclodepolymerised using 2 mol% of dibutoxydibutyltin (9) as the catalyst in chlorobenzene at re¯ux temperature for 8 h to give the corresponding cyclic oligomers (3)±( 5) in good yields.…”

Permanganate–periodate oxidation. Part VIII. The oxidation of some cyclic mono-olefins and monoterpenes

“…With these two terpenes it is possible that a reactive inethylene group is produced which is oxidized further and may thus lead to a variety of products. Also, one cannot rule out the formation of oxides, as found by Klein and Rojahn (2) in the permanganate oxidation of 1,5-dienes, by Apsimon et al (3) in the oxidation of methyl pimarate, and by us (4) in the oxidation of occidentalol. When the oxidation of menthone was carried out with different amounts of potassium carbonate, similar results (Table 11) as those with cyclohexanone were obtained (see Table I).…”

“…In a preliminary experiment it was found that a-terpineol did not give a high yield of the expected product, homoterpenyl methyl ketone. In view of this, and of the different behavior of some dienes as reported recently by Klein and Rojahn (2), Apsimon et al (3), and von Rudloff (4), the oxidation of some cyclic monoterpenes and related cyclo-olefins was studied with the specific purpose of determining whether or not the cyclic mono-olefins, and in particular monoterpenes, would react as predicted with the permanganate-periodate reagent.…”

Postulated intermediates and activated complexes in the permanganate ion oxidation of organic compounds

“…Alternatively, permanganate ion would attack the sulfur atom of the thiocarbonyl group or mecaptan 101a, 10lb.The kinetics and mechanisms of the permanganate ion oxidation of thiocarbonyl compounds, thiols, sulfides, sulfoxides, disulfides, sulfinic acids, and sulfenic acids are under investigation TM'; 3 o XIII. PERMANGANATE ION-PERIODATE ION SYSTEM a9,[231][232][233][234][235][236][237][238][239][240][241][242][243] Cleavage of carbon-carbon double bonds takes place smoothly with periodate ion and catalytic amounts of permanganate ion in neutral solution231-243. This general method is useful both preparatively and analytically.…”