L,ll-Dien-6-ynes

Starting from suitably substituted 2-bromotrideca-l,ll-diene-6-ynes, an all-intramolecular domino Heck-Diels-Alder reaction can occur which features the formation of even four rings. When (E/Z)-125 is treated with... 

In more complex reaction cascades an additional alkyne-insertion step can occur. Thus starting with intramolecular carbopalladation of a vinyl iodide to a carbon-carbon triple bond, followed by two intramolecular alkene-insertion steps and termination with dehydropalladation, a palladium-catalyzed synthesis of l-(5 -methylbicyclo[3.1.0]hex-T-yl)-5,5-bis(carboethoxy)cyclo-hexadiene (52) starting from l-iodo-4,4-bis(carboethoxy)-ll-methyldodeca-l,ll-dien-6-yne (51) is achieved. ... 

The 2-bromododeca-l,ll-dien-6-yne derivative 461 undergoes a triple cyclization, followed by rearrangement, under the influence of a palladium catalyst to yield 462. Cross-coupling of the iodo compound 463 with ( )-l-hexen-l-ylzinc chloride in the presence of tetrakis(triphenylphosphine)palladium yields 68% of the indane 464 and 19% of the uncyclized product 465 ". ... 

Another potentially powerfnl sequence arises by combining one or two intramolecular Heck-type couplings with an intra- or intermolecular Diels-Alder addition (for early examples of inter-intermolecular one-pot domino Heck-Diels-Alder reactions see Refs. [49] and [50]). An all-intramolecular version of such a sequence has been shown to proceed reasonably smoothly for terminally alkoxycarbonyl-substituted 2-bromotrideca-l,ll-dien-6-ynes under palladium catalysis at 130 °C. At 80 °C, the sequential reaction stops after the two consecutive Heck-type cyclizations and subsequent /3-hydride elimination to give a 1,3,6-triene apparently only the ( )-isomer undergoes the intramolecular Diels-Alder reaction, as the (Z)-l,3,6-triene is observed accompanying the tetracyclic system obtained at 130 °C (Scheme 36). 

An interesting sequence of two consecutive Heck-type cyclizations and a subsequent Diels-Alder addition was observed, when the methoxycarbonyl-substituted 2-bromo-trideca-l,ll-dien-6-yne E/Z)-77 was treated with a typical palladium catalyst [318] (Scheme 8.20). The cyclization of dienyne 77 at 80°C gave two diastereomeric trienes ( /Z)-78. At higher temperature (130°C), an intramolecular... 

For the construction of highly condensed oHgocychc skeletons, the cascade consisting of two intramolecular Heck-type reactions and a 6 r-electrocychzation as performed with the 2-bromododeca-l,ll-dien-6-ynes ( )- and (Z)-89 to yield tetracycles cis- and trans-90, respectively, is particularly elegant (Scheme 8.23) [318]. 

An alkynylcyclopropane was also formed on heating a 10-selena-l 1,12-diazatricyclo[6.3.0.0 ]-dodeca-l(9),ll-diene under reduced pressure to give bicyclo[6.1.0]oct-2-yne in 21% yield. When the thermolysis was carried out in the presence of 2,3,4,5-tetraphenylcyclopenta-2,4-dienone, the alkyne underwent a Diels-Alder reaction subsequent decarbonylation gave 10,11,12,13-tetraphenyltricyclo[6.4.0.0 ]trideca-l (9),10,12-triene. ... 

The use of tandem reactions continues to be an efficient method for the construction of complex molecules. While tandem cyclization reactions such as the reaction of do-deca-l,6-dien-ll-yne (29) with Et3B-Ph3SnH to furnish the products (30)-(32)... 

J. Marco-Contelles, Synthesis of polycyclic molecules via cascade radical carbocycliza-tions of dienynes the first SnPh3 radical-mediated (2 + 2 + 2] formal cycloaddition of dodeca-l,6-dien-ll-ynes, Chem. Commun. (Cambridge), (1996)2629-2630. 

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