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...

Some chemistry of the a-and 0-epoxides derived from a methyl pimarate degradation product (vinyl group transformed into a methoxycarbonyl) is described. The a-epoxide was found to be a very reactive species leading, by an intramolecular process, to a hydroxy-y-lactone even on standing in hexane solution. A possible explanation for the reactivity is given, based on a conformational argument. The P-epoxide undergoes a cleavage reaction with Lewis acid to give a 'backbone' rearrangement product, although a non-rearranged compound was obsemed in minor yield.Canadian Journal of Chemistry. 47,2859Chemistry. 47, (1969 In Part I1 of this series (1) we described the formation of an epoxide 1 during the Lemieux oxidation (2) of methyl pimarate 2. In this paper we describe some chemistry of the decarbonylated esterified derivative of 1, i.e. epoxide 3, and of its a-epoxy isomer 4a synthesized previously (1) in our structural studies. We also present further evidence for the structural assignments for these compounds.hindered side of the molecule. It is interesting to compare the nuclear magnetic resonance (n.m.r.) spectra of 3 and 4 where the signals for the C-14 protons appear at 2.75 and 3.25 6 respectively. Inspection of models shown here in the perspective drawings 5 and 6 reveal that in the a-oxide6aa, the 14P-proton is always adjacent to the ester group, and would thus be subject to an extra deshielding effect by this group, a juxtaposition not possible in 5 (a).' Epoxide 4a is a very labile compound and rearranges even on warming in hexane to a new material m.p. 215 "C analyzing for C20H3005. Some Reactions of a-Epoxide 4a'The conformation 6 representing the a-epoxide is only that which we considered in our early n.m.r. assignmentsIn Our we proposed the strut-since it seemed the most logical at the time. However, as ture of 3 derived from 1 on the basis of a synthesis the chemistry described here has led us to propose that from a methyl pimarate degradation product and this compound exists as 9 the n.m.r. arguments could be in question. But examination of Dreiding models indito the a-e~oxide 4a. This last cates that, regardless of the conformations taken up by compound was obtained by epoxidation of the the B and C rings, there still exists a difference in the corresponding olefinic material assuming that the degree Of ecllpslng of the CH bond and the rnethoxycarbonyl grouping sufficient to distinguish approach of epoxidizing agent was from the least between the a-and P-epoxides.Can. J. Chem. Downloaded from www.nrcresearchpress.com by 18.236.120.13 on 05/11/18For personal use only.

The oxymercuration-demercuration procedure was explored for methyl pimarate and methyl sandaracopimarate. In the first case a dimercurial-monoether was obtained yielding a cyclic ether on demercuration. In the second, a monomercurial was obtained arising from attack on the vinyl group only, and demercuration gave a mixture of alcohols which were oxidized to a methyl ketone, which on hypoiodite degradation yielded a known degradation product of methyl sandaracopimarate. The difference in behavior between the two series is attributed to the proximity of the double bonds in methyl pimarate.CanadIan Journal of Chemistry, 47,2865Chemistry, 47, (1969 As part of our studies on pimaric l a and sandaracopimaric acid 2a (1, 2) we were interested in two aspects of their chemistry. Firstly we wished to epoxidize the vinyl groups preferentially in order to study their cleavage in the vicinity of the nuclear double bonds, and secondly we were intrigued by the interaction of the double bonds in pimaric acid as compared with sandaracopimaric acid, as evidenced by unusual oxidation products (1).Normal epoxidation of the parent acids or their methyl esters led exclusively to epoxidation of the nuclear double bond (3, 4), and attempts at bromohydrin formation (5) were inconclusive. Thus we felt that perhaps the oxymercuration procedure (6) would lead to preferential vinyl attack, and this process might also provide us some further information on the spatial interaction of the two double bonds in 1 (7). Oxymercuration-demercuration of MetlzylPirnarate l b Reaction of methyl pimarate l b with one equivalent of mercuric nitrate or mercuric acetate in aqueous t-butyl alcohol resulted in about 50% conversion to an oxymercurial isolated at its chloroderivative (see Experimental). When two equivalents of mercuric nitrate were used, about 90 % conversion was observed.The crystalline chloromercurial analyzed for C21H3203Hg2C12 m.p. 176", its infrared (i.r.) spectrum indicating no hydroxyl absorption but ester absorption was evident at 1726 cm The nuclear magnetic resonance (n.m.r.) spectrum showed no signals for olefinic protons. Assuming Markofinikov-type addition of the mercury salts (6) then these facts are best accommodated by structure 3. The n.m.r. spectrum of 3 supported the structural assignment as follows.Centered at 3.9 6 was a doublet of doublets characteristic of the X branch of an ABX system with JAx 6 Hz and JBx 11 Hz which we assign to the H-15 proton of 3. At 3.0 6 there was a weakly coupled singlet (J 0.2 Hz) which we assign to. H-14P appearing at a lower iield than the C-16 protons since it is both tertiary and will be affected somewhat by the proximate ether bridge. The coupling observed is probably due to W-plan coupling (8) with the 12P proton.The stereochemistry at C-14 is assumed since the intramolecular attack on a mercurinium ion (6, 9) at C-8 and C-14 must come from the opposite face than the mercury (lo), and the stereochemistry of pimaric acid fixes the direction of attack from the p face by the two carbon Can....