Iron porphryin complexes are active catalysts for the cyclopropanation of alkenes by ethyl diazoacetate. Fe(TIP) (TIP = meso-tetra-p-tolylporphyrin), an isolated iron(II) porphyrin complex, can be used as the catalyst, or the iron(III) complexes of several porphyrins can be reduced in situ. The reactions produce synthetically useful excesses of the trans cyclopropyl ester products. This stereoselectivity exhibits a modest solvent dependence, with donor solvents giving higher ratios of the trans cyclopropane products. The diastereoselectivity exhibits only a modest dependence on the steric bulk of the porphyrin. The reactions are selective for 1-alkenes and 1, 1-disubstituted alkenes. Conjugated substrates and enol ethers react more rapidly than simple aliphatic alkenes. A mechanistic model for the iron-mediated reactions is proposed which is consistent with the data presented herein. Disciplines Chemistry CommentsReprinted (adapted) Am. Chern. Soc. 1995, 117, 9194-9199 Shape Abstract: Iron porphryin complexes are active catalysts for the cyclopropanation of alkenes by ethyl diazoacetate. Fe(TIP) (TIP = meso-tetra-p-tolylporphyrin), an isolated iron(II) porphyrin complex, can be used as the catalyst, or the iron(III) complexes of several porphyrins can be reduced in situ. The reactions produce synthetically useful excesses of the trans cyclopropyl ester products. This stereoselectivity exhibits a modest solvent dependence, with donor solvents giving higher ratios of the trans cyclopropane products. The diastereoselectivity exhibits only a modest dependence on the steric bulk of the porphyrin. The reactions are selective for 1-alkenes and 1, 1-disubstituted alkenes. Conjugated substrates and enol ethers react more rapidly than simple aliphatic alkenes. A mechanistic model for the iron-mediated reactions is proposed which is consistent with the data presented herein.The metal-catalyzed cyclopropanation of substituted olefins by diazo esters is a reaction commonly employed in organic synthesis. 1 Chiral copper 2 -4 and rhodium 5 • 6 catalysts have recently been reported to effect cyclopropanation with high enantioselectivity. However, the diastereoselectivities obtained in these reactions are generally poor. Mixtures of the trans and cis cyclopropyl esters are produced, with the trans isomer obtained in only a slight excess. A notable exception is a recently reported ruthenium catalyst/ which provided high enantioselectivities and trans/cis ratios of 10:1 using ethyl diazoacetate (EDA) as the carbene source.We are interested in the development of metalloporphyrin cyclopropanation catalysts, since such reactions often exhibit unique stereoselectivities and exceedingly high catalyst turnover numbers. For example, rhodium(III) porphyrin-catalyzed cyclopropanation reactions using EDA as the carbene source produced the cis cyclopropyl ester as the major product when bulky ligands such as the tetramesitylporphyrin (TMP) (see Figure 1) were employed. 8 -11 To the best of our knowledge, this is the only exampl...

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SummaryThe Rhodobacter sphaeroides photosynthesis response regulator, PrrA, positively regulates cycA P2 expression. Deletion analysis has identi®ed sequences within 73 bp upstream of the transcription initiation site that are required for the activation of cycA P2 by PrrA. A mutant form of the Rhodobacter capsulatus PrrA homologue, whose activity is independent of phosphorylation (RegA*), protects an < 26 bp region of cycA P2 that is centred at < À50 from DNase digestion, and activates transcription of a mutant À14T promoter with increased activity when using either R. sphaeroides RNA polymerase or Escherichia coli Es 70 . A 4 bp target site mutation that eliminated DNA binding and transcription activation by RegA* in vitro also abolished PrrA activation of cycA P2 transcription in vivo, indicating that this region contains a PrrA binding site. By analysing the behaviour of the À14T mutant cycA P2 promoter in vivo, we also found that PrrA uses the same target site to activate expression in both the presence and the absence of O 2 . However, the extent of transcription activation by PrrA at cycA P2 in vivo is greater under anaerobic conditions.

An array of neutral borabenzene−ligand complexes (ligand = pyridine, 2,6-lutidine, NEt3, PMe3, CN-t-Bu) have been synthesized in three straightforward steps from commercially available 1-(trimethylsilyl)-1,4-pentadiyne. An X-ray crystal structure of borabenzene−PMe3 is reported.

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