Cyclic manganate diesters

Products. The work of Wagner (42,43) and Boeseken (44) established that the oxidation of alkenes under alkaline conditions results in a syn-addition of two hydroxyl groups. In order to account for this observation, Wagner suggested that the reaction must proceed by way of an intermediate cyclic manganate(V) diester, 1, as in equation 3. 

The evidence supporting the suggestion that cyclic manganate(V) diesters are intermediates in the reaction between alkenes and permanganate is compelling (47), and Simandi (48) has also suggested that a similar intermediate, 2, may occur during the oxidation of alkynes as in equation 4. 

Conversion of 4 into a cyclic manganate(V) diester which was discussed above, then requires migration of the carbon from manganese to oxygen as in Equation 6. 

It is a useful oxidant for hydrocarbons, alkenes, alcohols and aldehydes. Permanganate reacts with carbon-carbon double bonds to form a cyclic manganate(V) diester. The nature of the products is determined by subsequent rapid processes. 

The cyclic manganate(V) diester anion 57 formed in a [3 + 2]-cycloaddition is believed to be the intermediate in the oxidation process434 (Scheme 9.9). This intermediate may be formed through the rearrangement of oxametallacyclobutane 58 resulting from a [2 + 2]-cycloaddition,442,443 Experimental observations indicate that the product 1,2-diol is formed as a result of the gradual reduction of the cyclic... 

As depicted in equation (20), the addition of a phase transfer agent, (eg. quaternary ammonium or phosphonium ions), brings permanganate into solution in nonaqueous solvents. Once solubilized, it reacts with alkenes to produce an intermediate that has been characterized by Ogino et al. as a cyclic manganate(V) diester (9), that can be decomposed by acidic solutions to yield aldehydes or by mild base to give the cone KNiding a-diol, as in Scheme 1. 

In close analogy with the osmylation reaction, kinetic data are consistent with a mechanism involving initial reagent-substrate interaction to form a charge-transfer complex with subsequent breakdown via oxametallacyclobutane 1 to the metastable cyclic manganate(V) 2. This diester is believed to lead to the desired diol as well as to other alkene oxidation products. 

Oxidation of methyl( )-cinnamate with quarternary ammonium permanganates in CH2Cl2 is fastest for the ions which minimize the interionic distance in the quarternary ammonium ion pair. An inverse secondary deuteriom isotope effect was observed. The reaction is initiated by an electrophilic attack, followed by a slower conversion of a 7r-complex to a cyclic manganate(V) diester (2). 

---