Paul Binger

Cyclopropenes and methylenecylopropanes as multifunctional reagents in transition metal catalyzed reactions

The tremendous potential of cyclopropenes and methylene-cyclopropanes as multifunctional reagents in organic syntheses has only been recognized in the last decade. The use of transition metal catalysts allows an effective control of their transformations enabling highly selecitive syntheses ranging from three- to sevenmembered carbocycles. The activities in this field are summarized in this review for the first time with an emphasis on the preparative aspects of this work.

Metallacycloalkanes: I. Preparation and characterisation of α,α′-bipyridyl-5-nickela-3,3,7,7-tetramethyl-trans-tricyclo[4.1.0.02,4]heptane

Abstract Oxidative addition of 2 molecules of 3,3-dimethylcyclopropene (I) to α,α′-bipyridyl(1,5-cyclooctadiene)nickel(0) (III) gave the title compound (IV) in over 90% yield. Complex IV was characterized by mass, 1 H NMR and 13 C NMR spectroscopy. Its structure was determined by X-ray diffraction ( a 13.7081(2), b 14.638(2), c 9.5139(1) A, β 110.82(1)°, C 2/ c , R = 0.05 for 1614 reflections).

A Convenient Preparation of Trimethylborane and Triethylborane

Abstract A convenient, high yield preparation of Me3B on a laboratory scale from (n-BuO)3B and Me3Al2Cl3 is described. The preparation of Et3B from Al3Et and Et2O[sbnd]BF3 on a laboratory scale and from AlEt3 and KBF4 on a pilot plant scale are also given.

Organo-1,2-Phosphaboretene

Abstract Sodium trialyl-1-alkynylborates (I) react with chlorodiorganophosphanes to give organo-1,2-phosphaboret-3-enes (II) in high yields. However, organo-1,2- azaboret-3-ines cannot be prepared from I and e.g. chlorodiethylamine. Some reactions of the phosphaboretenes (II), such as transmetallation using triethylalane, oxidation with trimethylamine- N -oxide and protolyses to give E -alkenyl-phosphanes are described.

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.

Metallacycloalkanes : II. Reactions of α,α′-bipyridyl-5-nickela-3,3,7,7-tetramethyl-trans-tricyclo[4.1.0.02,4]heptane☆

The title compound (II) underwent reductive elimination on treatment with maleic anhydride, tetracyanoethylene or triphenylphosphite to give 3,3,6,6,-tetramethyl-trans-tricyclo[3.1.0.02,4]hexane (III). With triphenylphosphite bi(2,2-dimethylcyclopropyl) (V) and 1-(2,2-dimethylcyclopropyl)-3-methyl-1,3-butadiene (VI) were also formed. Acidolysis of II with either HCl, malonic acid or methanol gave V. An intermediate complex α,α′-bipyridyl(phenoxy)-3-nickel-1,1′-bi-(2,2′-dimethylcyclopropyl) (VIII) was isolated by reaction of II with phenol. Methylene dibromide reacts with II to give III and 3,3,7,7-tetramethyl-trans-tricyclo[4.1.0.02,4]heptane (IV). With triethylaluminum and II complete exchange of the alkyl groups occurred and V was released on hydrolysis. Trifluoroborane diethyl ether and II gave 3,3,6,6-tetramethylcyclohexa-1,4-diene in a rearrangement-displacement reaction. The cyclodimerisation of 3,3-dimethylcyclopropene (I) to III catalysed by II and the fact that II can be recovered from the reaction mixture provides strong evidence for the intermediacy of metallacyclopentanes in these transition-metal-catalysed [2π + 2π] cyclo-additions.

Preparation and characterisation of some 4,4-dimethylbuta-1,3-dienone-transition metal carbonyls

(4,4-Dimethylbuta-1,3-dienone)iron tricarbonyl (IIa) is obtained in 70% yield from 3,3-dimethylcyclopropene (I) and nonacarbonyldiiron and in 17% yield from I and pentacarbonyliron. Analogously (4,4-dimethylbuta-1,3-dienone)-(η5-cyclopentadienyl)manganese carbonyl (V) is formed from I and (η5-cyclopentadienyl)(tetrahydrofuran)manganese dicarbonyl. Complexes IIa and V have been characterised by physical and chemical methods. Triphenylphosphine displaces one CO ligand from IIa to yield the corresponding triphenylphosphine-iron complex. The structure of IIa has been determined by X-ray diffraction.

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.

Bis(2,4-di-t-butyl-η4-1,3-diphosphacyclobutadiene)nickel

t-Butylphosphaacetylene 2 reacted with nickel acetylacetonate/n-butyllithium to furnish the title compound 4, the structure of which has been elucidated by X-ray crystallography.

Synthesis of silylated methylenecyclopropanes

2-Trimethylsilylmethylenecyclopropane (=3) was synthesized by reaction of lithio methylenecyclopropane with TMSCl. The lithium salt of (=3) reacts with some electrophiles by α- or γ-attack depending on the nature of the electrophile. Whereas alkenylbromides 8 and 9 or alkinylbromide 10 give exclusively α-attack, benzaldehyde reacts with γ-alkylation.