DMPM

Cleavage of MPM, DMPM, and TMPM ethers with DDQ in CHzCIs/HzO at 20 ... 

This ether has properties similar to the p-methoxybenzyl (MPM) ether except that it can be repioved from an alcohol with DDQ in the presence of an MPM group with 98% selectivity The selectivity is attributed to the lower oxidation potential of the DMPM group 1.45 V for the DMPM versus 1.78 V for the MPM. 

Cleavage of MPM, DMPM, andTMPM Ethers with DDQ in CH2CI2/H2O at 20°... 

Mg(C104)2, hv, anthraquinone or dicyanoanthracene. " These conditions also cleave the DMPM group. 

Cleavage of the DMPM group is achieved by conversion with trifluoroacetic anhydride to the amide, which is then removed with NaBH4/EtOH (93-97% yield). "... 

Perreault, D., Drouin, M., Michel, A., Miskowski, V.M., Schaefer, W.P. and Harvey, P.D. (1992) Silver and Gold Dimers. Crystal and Molecular Structures of Ag2(dmpm)2Br2 and [Au2(dmpm)2] (PFe)2 and Relation between Metal-Metal Force Constants and Metal-Metal Separations. Inorganic Chemistry, 31, 695-702. 

The dimer [Ir(CO)2(dmpm)]2, (447), (dmpm = bis(dimethylphosphino)methane) is prepared via the reaction of [Ir(cod)Cl]2 and dmpm in toluene at 0 °C.748 (447) reacts with Me3NO and then further with C02 to produce a binuclear Ir1 complex (Reaction Scheme 50). 

We conclude that only one phosphine attacks a ji-S group of 20. Indeed, the phosphine sulfide product from dmpm is Me2P(S)CH2PMe2, not a bis(sulfide).The other phosphine implicated by Eqs. (32) and (33), whether from a second PR3 or from a di-phosphine, adds as a Lewis base to rhenium. The basis for this is that a pyridine easily replaced one of the phosphines in the mechanism. This proposed mechanism should steer the reaction directly towards formation of 21, but owing to the dilemma posed in point (c), an intermediate likely intervenes. It can partition to the slowly-reacting 21 or to 23, the latter step requiring additional phosphine Scheme 13 shows the postulated mechanism. The dual role for phosphine and the use of Py in its place and the proposal for partitioning are shown in Scheme 14. 

Scheme 13. Proposed mechanism for reactions of a using dmpm as an example.

The same authors also studied the related complexes [Au2(L-L)(i-mnt)] (L-L = dmpm, dppe i-mnt= S2C2(CN)22 ) [29], the first (dmpm complex) being a helical extended polymer and the second (dppe) a monomer. In the former, the intramolecular distances are 2.925(3)-2.893(3) A, and the intermolecular distances 3.171... 

Nomially, dry solvents are employed in the oxidation of unsaturated alcohols with DDQ. This is done because DDQ is decomposed by water.94c On the other hand, the use of wet solvents may not be deleterious, as a mixture of CH2CI2 and water is routinely employed for the deprotection of p-methoxybenzyl (PMB)10S and 3, 4-dimethoxybenzyl (DMPM)106 ethers with DDQ, and, when this deprotection leads to an unsaturated alcohol, a prolonged reaction allows a successful oxidation of the alcohol to a ketone.107... 

DDQ is a potent hydride abstractor with a great tendency to produce oxidations when an intermediate stable carbocation can be formed. That is why DDQ is able to remove p-methoxybenzyl (PMB),106 3,4-dime thoxyben-zyl (DMPM)106 and 2,4-dimethoxybenzyl (DMB)118 protecting groups under very mild conditions. 

A similar range of derivatives of Ti, Zr and Hf result as indicated in Scheme 7, and of particular interest are the reactions of 32 with DMPM to give the A-frame -like complexes 33 with disilyl selenide elimination97. 

---