L-Ene-6,12-diynes

Complementary cycloadditions of 7-ene-l,13-diynes proceed with similar success, and are noteworthy in their ability to incorporate tetrasubstituted alkenes with total diastereoselectivity (equation 24). Incorporation of the alkene into a heteroaromatic ring is compatible with all-intramolecular cycloadditions of this type as well (equation 25). ... 

Hexadehydro-[ 18]annulene 80>, 15, (see Table 4) possesses no inner protons and the six equivalent outer protons resonate at t 2.98. This represents a downfield shift of over 1 ppm from a model compound, cis-hex-3-ene-l,5-diyne, 9, (t 4.11). This model compound also served to clarify the interpretation of the singlet at t 5.55 in the case of l,5,9-tridehydro-[12]annulene, 1, a molecule for which aromaticity is not predicted. The downfield shift of 15 and the upfield shift of 1 from the acyclic model can then be attributed to a diamagnetic ring current in 15 and a paramagnetic ring current in 1. 

Echinacea pallida roots contain a high amount (0.2-2.0%) of essential oil [5, 14, 15, 21, 67-69]. Main constituents are pentadeca-8Z-en-2-one [19], pentadeca-1, 8Z-diene (44% of the oil) and 1-pentadecene (Fig. 1) [17, 70]. In addition, pen-tadeca-8Z,llZ-dien-2-one, pentadeca-8Z, 13Z-dien-ll-yn-2-one and tetradeca-8Z-en-ll,13-diyn-2-one are occurring [14] and probably also (E)-lO-hydroxy-4,10-dimethyl-4,ll-dodecadien-2-one ( echinolon ) [18]. These ketoalkenes and ketoalkynes are also the major lipophilic constituents of . pallida roots. Other constituents of this type are pentadeca-8Z-ene-ll,13-diyn-2-one, pentadeca-8Z,11Z, 13 -triene-2-one, and pentadeca-8Z,ll ,13Z-triene-2-one (Fig. 7) [12, 19, 71]. According to Schulte et al. [19], who probably examined . pallida instead of . angustifolia only 2 mg% polyacetylenes (calculated on airdried material) with trideca-l-en-3,5,7,9,ll-pentayne and ponticaepoxide as main compounds are present. 

Occurring Acetylene Compounds. XXVII. The Synthesis of a Mixture of Trideca-1.3,1l-triene-5,7,9-triyne (II) and trans-l-Phenylhepta-l,3-diyn-5-ene (V). A Novel Cyclisation Reaction. Acta Chem. Scand. 13, 2101 (1959). 

For example, the octahydrophenanthrene skeleton 237 was obtained from the 2-bromotetradeca-l-ene-7,13-diyne 233 when the triple bond was terminally substituted by a trialkylsilyl group. Formation of the benzene rings 237 at the last step can be understood either in terms of 67T-electrocyclization of the intermediate 234 to yield 235, followed by /S-H elimination, or 6-endo-trig cyclization of 234 to produce 236 and fi-Yi elimination. 

The octahydrophenanthrene skeleton is also formed from 2-bromotetradeca-l-ene-7,13-diynes with a trialkylsilyl-substituted terminal triple bond (Scheme 46, Eq. 1). With an unsubstituted terminal acetylene, the same bromoenediynes yield bisannelated ful-venes by a completely different cascade carbopalladation mode involving a 5-exo-trig cy-clization and a [l,5]-sigmatropic shift of the CH2PdBr group or a 3-exo-trig cyclization... 

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