Ungewöhnliche intra- und intermolekulare palladiumkatalysierte Kupplungsreaktionen mit tetrasubstituierten Alkenen vom Methylencyclopropan-Typ

Intermolecular Heck Coupling with Hindered Alkenes Directed by Potassium Carboxylates

Pd⁰ -catalyzed Mizoroki-Heck reactions traditionally exhibit poor reactivity with polysubstituted, unbiased alkenes. Intermolecular reactions with simple, all-carbon tetrasubstituted alkenes are unprecedented. Herein we report that pendant carboxylic acids, combined with bulky monophospine ligands on palladium, can direct the arylation of tri- and tetrasubstituted olefins. Quaternary carbons are established at high Fsp³ attached-ring junctures and the carboxylate directing group can be removed after coupling. Carboxylate directivity prevents over-arylation of the new, less substituted alkene, which can be diversified in subsequent reactions.

First Comprehensive Investigation of Suzuki Couplings of Alkenyl Nonaflates with Aryl and Alkenyl Boronic Acid Derivatives by Using Classical Conditions and Microwave Heating

Alkenyl nonaflates (nonafluorobutanesulfonates) are excellent substrates in a variety of palladium-catalysed coupling reactions. We herein demonstrate that bicyclic nonaflates generated from 8-heterobicyclo[3.2.1]octan-3-one derivatives can be coupled with aryl or alkenyl boronic acids in a very efficient manner. The resulting densely functionalised bicyclic skeletons are highly suitable for further synthetic elaboration. The thermal Suzuki couplings provided the expected products in moderate to good yields. Microwave (MW) irradiation dramatically shortened reaction times and gave superior results. Bisboronic ester 19 was also coupled with bicyclic nonaflates, for example, with 14, and double Suzuki-coupling products, such as 22, were isolated in good yields. We demonstrated the great synthetic potential of aryl-substituted 8-heterobicyclo[3.2.1]octene derivatives, such as 15, by the stereoselective conversion of this compound into highly substituted furanose 31 or substituted pyran derivative 33, which were obtained in short and efficient reaction sequences.

Diels–Alder Reactions of Novel (1′-Arylallylidene)cyclopropanes with Heterodienophiles

Palladium-catalyzed cross-coupling of various aryl iodides with bicyclopropylidene provided isolable (1'-arylallylidene)cyclopropanes, which reacted with a number of carbonyl compounds in the presence of Eu(fod)3 under high pressure to furnish oxaspiro[2.5]octene derivatives in moderate to good yields (22-69%). The reactions of the allylidenecyclopropanes with two azo compounds as dienophiles afforded diazaspiro[2.5]octenes in high yields (82 and 99%) even at ambient pressure. When treated with nitrosobenzene, two of the allylidenecyclopropanes gave the Diels-Alder adducts in up to 83 and 40% yield. 2,5-Diiodo-p-xylene coupled twice with bicyclopropylidene, and the product underwent a twofold Diels-Alder reaction with nitrosobenzene to produce the bis(spirocyclopropaneoxazine) derivative in 88% yield. This overall transformation can be brought about in a one-pot, two-step operation by addition of the nitrosoarene to the reaction mixture immediately after formation of the allylidenecyclopropanes to furnish various 5-oxa-4-azaspiro[2.5]oct-7-ene derivatives in 22-77% yield. The coupling of methyl bicyclopropylidenecarboxylate with 2,6-dimethylphenyl iodide produced a mixture of very stable regioisomeric allylidenecyclopropane derivatives in 90% yield. The reaction of this mixture with N-phenyltriazolinedione gave a corresponding mixture of the spirocyclopropanated heterobicycles in 61% yield.

The virtue of palladium-catalyzed domino reactions - diverse oligocyclizations of acyclic 2-bromoenynes and 2-bromoenediynes

The domino-type combination of consecutive palladium-catalyzed cross-coupling reactions with subsequent pericyclic transformations offers a very fast access to various oligocyclic skeletons. This Account highlights all-intramolecular, intra-intermolecular, and all-intermolecular organopalladation cascades leading to 1,3,5-hexatrienes, which undergo consecutive 6pi-electrocyclizations with closure of three, two, or just one ring, respectively. Sequences of cross-coupling reactions and Diels-Alder additions are also discussed, as well as tricyclizations of 2-bromoenediynes giving rise to bisannelated benzene and fulvene derivatives.

Organolanthanide-Mediated Ring-Opening Ziegler Polymerization (ROZP) of Methylenecycloalkanes: A Theoretical Mechanistic Investigation of Alternative Mechanisms for Chain Initiation of the Samarocene-Promoted ROZP of 2-Phenyl-1-methylenecyclopropane

A detailed theoretical investigation of alternative mechanisms for chain initiation of the organolanthanide-promoted ring-opening polymerization of 2-phenyl-1-methylenecyclopropane (PhMCP) with an archetypical [Cp2SmH] model catalyst is presented. Several conceivable pathways for important elementary steps, which also included ring-opening isomerization of PhMCP to phenylbutadienes, were critically scrutinized for a tentative course of the catalytic reaction. The operative mechanism starts with the first exo-methylene C=C insertion into the Sm-H bond in a 1,2 fashion and is followed by shift-based beta-alkyl eliminative cyclopropyl ring opening by cleavage of a proximal bond, while the alternative mechanism that commences with 2,1-insertion and subsequent ring opening by distal bond scission is revealed to be almost entirely precluded. The facile and irreversible insertion process is not found to occur in a regioselective fashion. The ring-opening process is analyzed as the critical step that discriminates between the two conceivable mechanisms. Opening of the cyclopropyl ring is kinetically easy and proceeds readily for the 1,2-insertion species, while a prohibitively large barrier must be overcome for ring opening of 2,1-insertion species. The isomerization of PhMCP in a ring-opened fashion, which would afford phenylbutadienes as possible products, is predicted to be a less likely process, owing to both kinetic and thermodynamic factors. The phenyl functionality has been demonstrated to distinguish between the regioisomeric ring-opening pathways, both kinetically and thermodynamically, thereby rendering this process selective with regard to the regiochemistry. Overall, chain initiation of the samarocene-mediated ring-opening polymerization of PhMCP is predicted to be a smooth, kinetically facile process.