Anthony J. Pearson

A new method for the oxidation of alkenes to enones. An efficient synthesis of Δ5-7-oxo steroids

A variety of cycloalkenes were converted into α,β-unsaturated ketones using t-butyl hydroperoxide in the presence of chromium hexacarbonyl catalyst. The scope of the reaction has been partly investigated, and it was found that the allylic oxidation proceeds selectively in the presence of some secondary alcohols. High-yield conversions of steroidal 5,6-enes into the corresponding 5,6-en-7-ones are reported.

Oxidation of alkenes to enones using tert-butyl hydroperoxide in the presence of chromium carbonyl catalysts

Abstract Treatment of alkenes with t-butyl hydroperoxide in the presence of Cr(CO) 6 or Cr(CO) x (CH 3 CN) y species results in oxidation of allylic methylene groups to give α,β-unsaturated ketones, selectively in the presence of certain alcohols, and in moderate to excellent yields.

N-Prolinylanthranilamide Pseudopeptides as Bifunctional Organocatalysts for Asymmetric Aldol Reactions

Proline anthranilamide-based pseudopeptides were shown to be effective organocatalysts for enantioselective direct aldol reactions of a selection of aldehydes with various ketones with excellent yield, enantioselectivity up to 99% and anti to syn diastereoselectivity up to 25:1.

Intramolecular alkyne–alkyne and alkyne–alkene couplings promoted by iron carbonyls

The first examples of iron carbonyl-promoted intramolecular coupling of alkyne and alkene, giving rise to cyclopentenones, are described.

Studies on ristocetin A. A synthesis of protected ristomycinic acid using organomanganese chemistry

Abstract Aryl ether formation by reaction of phenoxide nucleophiles with chloroarene-Mn(CO)3 cationic complexes, followed by reaction of the aryloxyarene-Mn(CO)3 complex with chiral glycine enolate equivalents, provides methodology for the synthesis of protected ristomycinic acid derivatives in a state of high optical purity.

Studies on the applications of arene-ruthenium complexes in synthetic approaches to vancomycin: a mild procedure for the selective formation of chlorinated aryl ethers and triaryl diethers

Abstract Reactions of ( η 6 -1,3-dichlorobenzene)( η 5 -cyclopentadienyl)ruthenium hexafluorophosphate and ( η 6 -1,3-dichloro-2-methoxy-benzene)( η 5 -cyclopentadienyl)ruthenium hexafluorophosphate with ortho-chlorinated phenolates were found to proceed with excellent selectivity to generate monoarylated ethers under mild conditions. The second halogen may be displaced allowing the synthesis of unsymmetrical and symmetrical triaryl diethers. Methodology for sequential selective displacement of both chlorides by different nucleophiles and a photochemical method for demetallation of the arene-Ruthenium-Cp ( η 5 -cyclopentadienyl) complexes are reported.

New strategies for the construction of macrolide antibiotic subunits using organoiron precursors

Abstract Tricarbonyldienyliron complexes 6 , 7 and 17 are used as precursors to a range of dienylacetic acid derivatives which are not readily available from other sources. The phenylselenolactonization of these dienes occurs in a regio- and stereocontrolled manner with conjugate attachment of a PhSe group anti to the lactone moiety in the case of cyclohexadiene derivatives. Oxidation of the allylic selenium compounds occurs with concomitant selenoxide (2,3)-sigmatropic rearrangement to give hydroxylactones.

A mild procedure for the selective formation of aryl ethers and triaryl diethers using arene–M–CP cations (M = Fe, Ru; Cp =η5-cyclopentadienyl)

Reaction of (η6-1,3-dichlorobenzene)(η5-cyclopentadienyl)iron hexafluorophosphate with aryl oxides from protected tyrosines proceeds under mild conditions to generate aryl ethers, and the halogens may be displaced sequentially, allowing the preparation of unsymmetrical or symmetrical triaryl diethers; (η6-N-acetyl-4-chlorophenylalanine methyl ester)(η5-cyclopentadienyl)ruthenium hexafluorophosphate was prepared and was shown to react with protected tyrosine aryl oxide to generate dityrosine derivatives, and a mild photochemical method for demetallation of the arene–M–Cp (Cp =η5-cyclopentadienyl) complexes is described.

Natural products synthesis using organoiron complexes

A survey is presented of applications of dienyl—Fe(CO)2L complexes as intermediates for natural products synthesis, based on (a) complexes which act as cyclohexenone y—cation equivalents, and (b) the ability of the metal to direct stereochemistry of C—C bond formation in seven— membered rings. This paper provides the opportunity to give a brief review of some of our work carried out at Cambridge University, England, during 1981—82, together with a progress report on some new projects which were initiated in October 1982, subsequent to moving to Case Western Reserve University. The work at Cambridge was based on the utilisation of cyclohexadienyl—Fe(CO)3 complexes of type 1 which we have now established as synthetic equivalents of cyclohexenone— y—cations (1), e.g. 2. Thus, reaction of lwith nucleophiles usually occurs regioselectively to give complexes of type 3, which are readily converted to cyclohexenones 4. It is appropriate to discuss the application of this concept to a total synthesis of the Aspidosperma alkaloid (±)limaspermine 5, since this piece of work illustrates a number of interesting aspects of reactivity, and methods which can be used to control regioselectivity during manipulation of diene and dienyl complexes of iron (2).

Crown-annelated p-phenylenediamine derivatives as electrochemical and fluorescence-responsive chemosensors: cyclic voltammetry studies

Cyclic voltammetry studies on crown-annelated tetraalkyl-p-phenylenediamine derivatives, in the presence of metal mono- and dications, reveal high selectivity toward dications, of potential value for the development of electrochemical sensors.