Catalytic Photoinduced Charge-Transfer Osmylation: A Novel Pathway from Arenes to Cyclitol Derivatives
✍ Scribed by Prof. William B. Motherwell; Alvin S. Williams
- Publisher
- John Wiley and Sons
- Year
- 1995
- Tongue
- English
- Weight
- 367 KB
- Volume
- 34
- Category
- Article
- ISSN
- 0044-8249
No coin nor oath required. For personal study only.
✦ Synopsis
The ability of the enzymatic system present in strains of Pseu-Lioniontrs pirtirfrz to achieve stereospecific vicinal cis dihydroxylation"' of benzene has spawned recent intense interest among synthetic organic chemists. The resultant cis diene diol and functionalized chiral derivatives have been widely used as starting materials for the syntheses of a diverse array of biologically important molecules including conduritols, inositols. prostaglandins, and
It was therefore of interest to devise a simple chemical method for the production of these useful building blocks. particularly since the commonly encountered reagents for in vitro oxidation of arenes, such as ozone and ruthenium tetraoxide, also lead to the concomitant cleavage of the carbocyclic ring. We now present the results of a preliminary study in which we have achieved the first direct metal-catalyzed. one-pot conversion of benzene and some simple arencs to conduritol and inositol derivatives.
The basia for our work rests on an elegant study by Kochi and Wallis.[s1 who demonstrated that actinic (UV) irradiation of the Electron Donor-Acceptor (EDA) complexrh1 ( I ) formed on mixing benzene and osmium tetraoxide led, in the presence of an excess of the OsO, and at a frequency equal or greater than that of the absorption maxima, to a polymeric 2:l adduct (4 Scheme 1 ) . which could be isolated as a monomer (5) by the 2 3 5 Scheme 1 addition of pyridine. The proposed mechanism involves photochemically induced charge transfer from the complex (1) to form an ion pair (2), which can collapse to the osmate ester of benzene diol (3) followed by a second thermal anti osmylation.
Although yields of the isolated adducts such as 5 were low even in the stoichiometric reaction, we envisaged that such a process could be made catalytic in osmium through careful selection of a suitable solvent system and oxygen atom transfer reagent. In this respect, since the heat of formation of the EDA complex between benzene and osmium tetraoxide has been estimated to be of the order of 0.5 kcalmol-t,[6' it was of paramount importance to avoid the use or generation of any molecule whose donor ability would give more stable OsO, [