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With use of a potentiometric procedure with quinone as reoxidant for Pd(O), the rate expression for allyl alcohol oxidation was determined to be rate = k[PdC1,2-][C6H60]/[H+] [C1-l2, an expression identical in form with that found previously for ethene and other acyclic olefin oxidations indicating similar mechanisms. The two trans attack mechanism suggested for acyclic olefin oxidation involve trans equilibrium hydroxypalladation and external hydroxide ion attack. In regard to the first, with most acyclic olefins the reversibility of the process cannot be determined. With allyl alcohol, however, the reversibility of hydroxypalladation can be tested by determining if allyl-1 , I d z alcohol (5a) isomerizes into an equilibrium mixture of 5a and dyl-3,3-d2 alcohol (5b) during the course of the oxidation. It was found that isomerization of 5a did not occur during oxidation so hydroxypalladation is nonreversible and the equilibrium hydroxypalladation mechanism cannot be operative. Next the possibility of external hydroxide was tested. The equilibrium formation of the intermediate r-complex PdC13(C6H60)-was studied by spectral means, and a value of 5 was found for the equilibrium constant, K,. As with other acyclic olefins, the value of K 2 for formation of the second intermediate PdC12(C3H60)(H20) was too small to be measured W0.025). With use of the experimental values of k, K,, and K2, it could be calculated that hydroxide attack would have to be faster than a diffusion-controlled reaction and thus impossible. Thus both reasonable trans attack mechanisms can be eliminated for allyl alcohol.

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The aerial parts of Vicoa pentanema yielded four new sesquiterpene lactones, namely, 10α-hydroxy-14H-inuviscolide (1), 4α,5α-epoxy-10α,11β,13H,14H-1-epi-inuviscolide 3-β-d-glucoside (2), 2α-O-acetyl-3β-hydroxyalantolactone (3), and 2α,3α-dihydroxyalloalantolactone (4). The structure and stereochemical assignments of all sesquiterpenes were based on their 1H and 13C-NMR spectral data, including those derived from 2D-NMR COSY, HETCOR, FLOCK, and NOESY experiments, as well as extensive NOE-difference studies. In addition, the same plant material yielded the known sesquiterpene lactones 8β-hydroxyparthenolide (5), 8-epi-confertin (6), 4α,5α-epoxy-10α,14H-1-epi-inuviscolide (7), inuviscolide (8), lipiferolide (9), and carabrone (10), the known thymol ester 7,8-epoxy-9-(isobutyryloxy)thymolisobutyrate (11), and its hydrolysis product 7-hydroxy-8,9-bis(isobutyryloxy)thymol (12).