Petra Wedemann

Palladium(0)- and Nickel(0)-Catalyzed [3 + 2] Co-Cyclization Reactions of Bicyclopropylidene with Alkenes

Bicyclopropylidene (1) readily undergoes a palladium(0)-catalyzed [3 + 2] co-cyclization with electron deficient alkenes (methyl acrylate, methyl trans-crotonate, methyl cinnamate and diethyl fumarate) as well as with some strained alkenes (norbornene, norbornadiene) by distal ring cleavage of one of the three-membered rings of 1. All these co-cyclizations are regioselective with respect to 1 as well as regio- and stereoselective with respect to the alkenes to give the corresponding 4-methylenespiro[2.4]heptane-trans-6-carboxylates 2a−5 with the electron deficient alkenes and the cycloadducts 6 and 7 with the strained alkenes in acceptable to good yields (56 to 83%). In contrast to palladium(0) catalysts nickel(0) complexes catalyze both distal ring opening of 1 and oxidative coupling of the two double bonds when 1 is reacted with e.g. diethyl fumarate. The result is a mixture of the methylenecyclopentane derivative 5 with the [2 + 2] cycloadduct 8 and the cotrimer 9.

Nanostructured nickel-clusters as catalysts in [3+2]cycloaddition reactions

Abstract Preformed Ni-clusters stabilized by tetraoctyl- or tetradodecylammonium bromide are readily available by electrochemical fabrication, the average size of the particles being 2.5 nm. Colloidal solutions of such clusters effectively catalyze the [3+2]cycloaddition of methylenecyclopropane to methyl acrylate. The preformed clusters can also be immobilized on solid supports, resulting in heterogeneous catalysts which also catalyze the cycloaddition reaction.

Nickel(0)-katalysierte [3+2]cycloadditionen von (diorganylmethylen)cyclopropanen mit elektronenarmen olefinen

Zusammenfassung [3+2]Cycloadditions of (diorganylmethylene)cyclopropanes (R = Ph; CH 3 ) with electron-deficient olefins are catalyzed by trisarylphosphite - Ni(0)-compounds to give (diorganylmethylene)cyclopentane derivatives in high yields.

Regioselektive [3+2] cycloadditionen von methylencyclopropan mit elektronenarmen olefinen an R3P-nickel(O)-katalysatoren

Abstract The triorganyl-phosphane/-phosphite-Ni(O) catalyzed [3+2]cycloaddition of methylenecyclopropane (=1) with electron deficient alkenes leads regioselectively to 2,3- or 3,4-disubstituted methylenecyclopentanes depending on the electronic properties of the olefin.

5-Alkylidene-hexahydro-1H-cyclopenta[c]pyrrol-1,3-diones by nickel(0) or palladium(0) catalyzed [3+2] cycloaddition of methylenecyclopropanes with maleimides

Abstract Nickel(0) catalyzed [3+2] cycloaddition of methylenecyclopropanes 1a - e with N-substituted maleimide 3b (R = CH 3 ) and 3c (R = Ph) leads almost exclusively to the title compounds 6 and 7 . The same reaction occurs in the presence of a palladium(0) catalyst with lower selectivity. Neither unsubstituted maleimide ( 3a ) nor maleic anhydride ( 2a ) undergo this metal catalyzed cycloaddition. With isopropylidenecyclopropane ( 1b ) an ene reaction takes place giving the codimers 4a,b, whereas (diphenylmethylene)cyclopropane ( 1c ) reacts in a Diels-Alder reaction with two equivalents of 2a , affording the cotrimer 5 .

1,1,3,3-Tetratriflylpropene (TTP): A Strong, Allylic C–H Acid for Brønsted and Lewis Acid Catalysis

Tetratrifylpropene (TTP) has been developed as a highly acidic, allylic C-H acid for Brønsted and Lewis acid catalysis. It can readily be obtained in two steps and consistently shows exceptional catalytic activities for Mukaiyama aldol, Hosomi-Sakurai, and Friedel-Crafts acylation reactions. X-ray analyses of TTP and its salts confirm its designed, allylic structure, in which the negative charge is delocalized over four triflyl groups. NMR experiments, acidity measurements, and theoretical investigations provide further insights to rationalize the remarkable reactivity of TTP.

The first metal complexes of bicyclopropylidene, a unique tetrasubstituted alkene ligand

The reactions of bicyclopropylidene 2 with bis(cyclopentadienyl)bis(trimethylphosphane)titanium( n II) 1 and with the cobalt chelate 4 give the first known metal complexes of bicyclopropylidene 3 and 7, respectively, in good yields; the bicyclopropylidene cobalt complex 7 is characterized by an X-ray crystal structure analysis which shows a severe out-of-plane bending of the alkenic ligand, indicating considerable back-bonding which goes along with a release of strain in the ligand.