Abstract
The compounds [3-(2-Bromocyclohex-2-enyloxy)prop-1-ynyl]-tert-butyl-dimethylsilane 3, [4-(2-bromocyclohex-2-en-1-yloxy)but-2-yn-1-yloxy]tert-butyldimethylsilane 5 and dimethyl 2-(2-bromocyclohex-2-enyl)-2-(3-(tert-butyldimethylsilanyl)prop-2-ynyl)malonate 9 were prepared and subjected to palladium-catalyzed intra-intermolecular cascade cross couplings incorporating bicyclopropylidene 10 under two types of conditions. In the presence of Pd(OAc)2, PPh3 and K2CO3 in acetonitrile at 80 °C, the products were indene analogues, cross-conjugated tetraenes 11, 12 and 13, respectively. The corresponding spirocyclopropanated tricycle 16 in dimethylformamide at 110 °C was obtained, albeit in low yield (24%), and observed as an equimolar mixture of diastereomers, whereas 14, 15 were not fully isolated.
Highlights
Palladium-catalyzed carbon-carbon bond forming reactions that involve carbopalladations of carbon-carbon double bonds can favorably be combined in all-intra, intra-inter- and intermolecular cascade reactions [5,6,7,8,9,10,11,12]
The so-called Mizoroki-Heck reaction, i.e., the palladium-catalyzed arylation or alkenylation of alkenes has been applied in a variety of new concepts [5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26]
In view of the steadily growing number of oligocyclic compounds with cyclopropyl moieties that show interesting biological activities [27,28,29], it is noteworthy and helpful that the highly reactive building block bicyclopropylidene 10 [30,31] can participate in various palladium-catalyzed cascade reactions to Molecules 2014, 19 furnish complex skeletons containing cyclopropyl groups [17,18,19,20] A high increase in molecular complexity can be achieved with sequential reactions starting with an intramolecular carbopalladation of a 2-bromo-1-ene-6-yne and trapping of the formed reactive vinylpalladium halide intermediate by bicyclopropylidene 10 and subsequent transformations [32]
Summary
Intra- as well as intermolecular so-called domino or cascade reactions is efficient in terms of increasing the molecular complexity in a minimum number of steps [1,2,3,4,5,6,7,8,9,10,11,12]. In view of the steadily growing number of oligocyclic compounds with cyclopropyl moieties that show interesting biological activities [27,28,29], it is noteworthy and helpful that the highly reactive building block bicyclopropylidene 10 [30,31] can participate in various palladium-catalyzed cascade reactions to Molecules 2014, 19 furnish complex skeletons containing cyclopropyl groups [17,18,19,20] A high increase in molecular complexity can be achieved with sequential reactions starting with an intramolecular carbopalladation (the first step of a Heck reaction) of a 2-bromo-1-ene-6-yne and trapping of the formed reactive vinylpalladium halide intermediate by bicyclopropylidene 10 and subsequent transformations [32]. Towards indene utilizing the thermal intramolecular Diels Alder cycloadduct As this cascade reaction principle appeared to deserve further development, we embarked on a project to prepare a few more 2-bromo-1-ene-6-ynes and employ them in palladium-catalyzed cocyclizations involving bicyclopropylidene 10
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