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[reaction: see text]. An efficient method for the in situ desilylation/oxidative dimerization of (trialkylsilyl)acetylenes is described. This protocol avoids the complications encountered with sensitive diynes by eliminating the deprotection and isolation steps. Various aromatic and alkyl diynes and tetraynes can be synthesized in a straightforward manner in good yields (82-99%) from TIPS-protected acetylenes. This method facilitates the efficient synthesis of novel tetrayne-bridged acetylenic cyclophanes 6 and 7 in a direct manner.

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, 183 (1984).Recent advances and examples of the intramolecular Diels-Alder reaction are summarized and applications to the total synthesis of natural products, both completed and in progress, noted. A detailed discussion of trienes leading to bicyclo[4.3.0]nonene skeletons is followed by examples of bicyclo[4.4.0]decenes and adducts arising from orthoquinodimethane precursors. Cycloadditions affording bicyclo[n.4.0] systems and bridged-ring adducts from cyclic dienes conclude this survey which is followed by a discussion of unreactive trienes and a brief analysis of synthetic strategy to complete the review. ALEX G. FALLIS. Can. J. Chem. 62, 183 (1984).On rCsume les recents dCveloppements et des exemples de rtaction de Diels-Alder intramolCculaire et on note leur utilisation dans la synthese des produits naturels dCjh effectuCs de m&me que dans celles qui sont en cours. Une discussion dCtaillCe des triknes conduisant aux squelettes bicyclo [Traduit par le journal]

Treatment of 5-bromo-1,3-pentadiene with indium metal in the presence of carbonyl compounds results in γ-pentadienylation to generate the 1,4-diene. Elimination of the resulting alcohol affords cross-conjugated triene systems which rapidly react with appropriate dienophiles to give tandem intermolecular Diels−Alder adducts.

A recent report by the present authors (Can. J. Chem. 56, 1020 (1978)) of the isolation of 7α-acetoxydihydronomilin from the seeds of Uncariagambia (Roxb.) contains a taxonomic error. The seeds were in fact from Xylocarpusgranatum (Koenig).

Four new classes of organic solvent soluble ethynylpentacene derivatives (2,9-, 2,10-, 2,6,9,13-, 2,6,10,13-) have been prepared by complementary, versatile, double Diels-Alder strategies. Functional groups on the A, C, and E rings can be manipulated to increase the solubility, modulate the electronics, and alter the solid-state packing. Cycloaddition reactions with diene 2 and 1,4,5,8-anthradiquinone (3) or ortho-quinodimethane 19 with 1-butyl-3-methylimidazolim iodide (18) as the iodide source (a significant improvement over NaI) and benzoquinone (20) followed by in situ aromatization afforded the quinones 4, 5, 21, and 22, respectively. For the 2,9- and 2,10- families, a one-pot desilylation/triflation was developed. Palladium(0) coupling and reductive aromatization afforded 2,9-di(triisopropylsilylethynyl)pentacene (10) and 2,10-di(triisopropylsilylethynyl)pentacene (11), respectively. Photodimerization of these pentacenes afforded the air-stable [4 + 4] cycloaddition pentacene precursors (tetrakisnaphthotricyclo[4.2.2.22,5]dodecanes, 12-15). Thermal cycloreversion of the dimers ( approximately 13 J/g, approximately 4 kcal/mol) produces the parent pentacenes (10 or 11). The tetrasubstituted family utilized a parallel route with extra versatility as the timing of the Grignard and palladium(0) coupling step may be varied depending upon the functional group combinations desired. The subsequent reactions provided the tetraethynylpentacenes 28-30, 33-35 (para-isomers), and 38 (meta-isomer). X-ray crystallography analysis of 28, 29, and 33 revealed various pi-pi stacked packing motifs that differ from the unfavorable herringbone pattern of pentacene.