Abstract:The structures and stereochemistry of 14 taxanes isolated from Taxus cunadensis have been rigorously established by high-resolution NMR techniques and mass spectrometry. Taus canadensis is the only yew that accumulates 9-dihydro-13-acetylbaccatin 111 (also called 7,9-deacetylbaccatin VI) as the most abundant taxane. Five 9-dihydrotaxanes derived from the Canadian yew are novel natural products not reported in the needles of other species of yew (8-11, 14, Fig. 1).

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1 (1990).The isolation and characterization of a novel triterpene glycoside from the sea cucumber Cucumariaji-ondosa, collected from the Gulf of St. Lawrence, are described. Physico-chemical data obtained on the underivatized saponin are presented in support of structure 1 for frondoside A. The structure is characterized by the presence of a branched oligosaccharidic chain composed of five units. The holostane-type aglycone features an endocyclic double bond at position C-7,8 and a P-acetoxy group at C-16. On dCcrit l'isolation et 1'Clucidation structurale d'un nouveau triterpkne-glycoside, obtenu de l'holothurie Cucumaria ji-ondosa provenant du golfe du St-Laurent. En se basant sur les donnCes physico-chimiques du produit intact, on propose la structure 1 pour le frondoside A. Le composC est caractCrisC par la presence d'une chaine oligosaccharidique branchke, de cinq unites. L'aglycone de type holostane posskde une insaturation en position C-7,8 et un groupement acCtoxy-P en C-16.

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The chemical composition of the essential oil of the needles and twigs of dwarf pine (Pinus mugo Turra) growing wild in Serbia was investigated. The oil was analysed by GC/MS and the major constituents found were δ δ δ δ δ-3-carene (23.9%), α α α α α-pinene (17.9%), β β β β β-pinene (7.8%) and β β β β β-phellandrene (7.2%).

Carbethoxymethyne (EtOCOC:) has been generated by the short wavelength photolysis of diethylmercury bisdiazoacetate, (N2CC02Et)2Hg + hv -* 2EtOCOC: + 2N2 + Hg, and its reactions with cyclohexene, c/s-2-butene, and rra«s-2-butene were investigated. The carbyne, formed in its 2 ground state, adds to the olefinic bond in a spin allowed but, according to INDO MO calculations, orbital symmetry forbidden concerted step with retention of the geometrical configuration of the parent olefin to yield a cyclopropyl radical. Parallel to addition, preferential insertion into the allylic C-H bonds also occurs yielding an alkyl radical. Thus, the basic chemical behavior of doublet ground state carbynes appears to bear a close resemblance to that of singlet carbenes. The cyclopropyl and alkyl radicals undergo free radical combination and hydrogen abstraction reactions with solvent molecules. The hydrogen abstraction reaction of cyclopropyl radicals is stereoselective and occurs from the sterically less hindered side of the ring, resulting in the preponderant formation of the less stable endo product. In the longer wavelength photolysis of the source compound N2 is eliminated in a stepwise fashion and a singlet state mercury carbene, which is capable of insertion and stereospecific addition, is formed. Cleavage of the C-Hg linkage in the source compound results in the formation of ethyl diazoacetate which was detected and monitored during the photolysis by infrared spectroscopy. The effect of conversion and wavelength of photolysis on product yields and the relative importance of the various competing primary modes of decomposition were investigated and the overall mechanism is discussed.arbon free radicals constitute the most common and frequently encountered class of organic intermediates. The chemistry of the trivalent, divalent, and to a lesser extent of the zerovalent carbon radicals, the simplest representatives of which are H3C•, H2C:, and the free carbon atom, respectively, comprises one of the fundamental pillars of modern organic chemistry. Little, however, is known about the family of monovalent carbon radicals, the carbynes. The simplest of

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