Mechanism of rhodium-promoted conversion of 3-vinyl-1-cyclopropenes to 1,3-cyclopentadienes. Stereochemistry of the carbon-carbon bond-forming step

Abstract

The above results suggest the following conclusions: (a) The carboxylate of Asp99 is able to carry out its function without forming H bonds to The phenolic hydroxyl of neither Tyr-52 nor Tyr-73 is catalytically essential even though they are absolutely conserved in groups I and I1 PLA2 sequences. (c) The aromatic rings of both residues are required, possibly for structural reasons. (d) If the H-bonding network shown in Figure The transition-metal-promoted reactions of cyclopropenes are of great synthetic utility and mechanistic interest.' We have demonstrated that 1,2,3-triphenyl-3-vinyl-l-cyclopropene undergoes a facile C-C cleavage reaction promoted by Pt(O), Rh(I),

Chemistry of Fischer-type rhenacyclobutadiene complexes. II. Reactions with alkynes and sulfonium ylides, and rearrangements induced by nitriles and pyridine

“…Schrock-type metal alkylidynes and metallacyclobutadienes react with alkynes also to yield g 5 -cyclopentadienylmetal complexes [11,12,17], and intermediacy of metallabenzenes has been proposed in some cases. However, other intermediates are possible as well [11,18].…”

Synthesis, Structure, Spectroscopy, and Reactivity of a Metallabenzene1

“…Structure and Spectroscopy of Iridabenzene 3. The solid-state structure of CHC(Me)CHC(Me)CHIr(PEt 3 ) 3 ( 3 ), determined by single-crystal X-ray diffraction, is shown in Figure ; selected bond distances and angles are given in the figure caption. The coordination geometry is square pyramidal, with C1, C5, P1, and P2 occupying the four basal sites and P3 residing in the axial site.…”

Iridium-Promoted Reactions of Carbon−Carbon Bonds. Skeletal Rearrangement of a Vinylcyclopropene during Iridacyclohexadiene Formation and Subsequent Isomerization of Iridacyclohexadienes via α,α‘-Substituent Migrations

“…For example, reductive elimination of bonds cd affords the vinylcyclopropene complex, elimination of bonds bc yields a metallacyclohexadiene, and coupling of bonds ad generates a coordinated cyclopentadiene; examples of all these reactions have been observed previously. [2][3][4][5][6][7][8][9][10][11][12][13][14][15] We believe this model is useful for understanding the chemistry described in this paper, in which we describe other skeletal contortions and substituent gymnastics observed in these systems. Skeletal rearrangements have been observed previously during the reactions of vinylcyclopropenes with transition metal complexes.…”

“…The ring opening of vinylcyclopropenes by transition metal complexes to give metallacyclohexadienes and related compounds is now well-established. [2][3][4][5][6][7][8][9][10][11][12][13][14][15] Metallacyclohexadienes are compounds of considerable interest, yet few isolated examples exist, and their reaction chemistry is poorly defined. They have been invoked as key intermediates in the Do ¨tz reaction, 16 and iridacyclohexadiene species, obtained by a different route, 17 were shown to undergo a facile deprotonation at the R-carbon to afford the first examples of iridabenzene complexes, leading to an extensive chemistry for these compounds.…”