Alkenes, viii functional groups

Another ruthenium-catalyzed oxidation uses tetrapropylammonium permthenate (TRAP) [24]. Being a ruthenium(VII) oxide, the permthenate ion is a less powerful oxidant than rutheni-um(VIII) oxide and more functional groups are stable to the oxidation conditions, including alkenes, alkynes, amines, amides, benzyl, trityl and silyl ethers [24]. However, alcohols and lactols still undergo oxidations in high yield with W-methyl-morpholine A-oxide (NMO) as the stoichiometric oxidant. The reactions are usually carried out in dichloromethane, acetonitrile, or mixtures of both in the presence of molecular sieves [24]. 

The synthesis of alkylidenes incorporating late transition metals has resulted in alkene metathesis catalysts having unprecedented functional group tolerance. In particular, the discovery that complexes of Group VIII transition metals were efficient ROMP catalysts introduced several advantages. Relative to their early transition metal counterparts, these classical catalysts functioned well in the presence of a variety of polar and protic functional groups (Table 2), and they functioned homogeneously in water. 

The hydrogenation of unsaturated aldehydes IV can be a complex transformation, as depicted in Scheme 2. Although the desired reactions are normally either the formation of allylic alcohol V, or saturated aldehyde VI, by 1,2 addition of hydrogen across the functional group, 1,4-addition across the conjugated functions can provide the enol, VII. Over-hydrogenation can result either in further saturation or, for allylic alcohols, hydrogenolysis to the alkene VIII (which can, in turn, be further saturated). 

Oxidation of alkenes with osmium(Vin) tetroxide (OSO4) (Chapter 6, Scheme 6.10) involves a cyclic intermediate and results in the addition of two hydroxyl groups to the same face [d5-, syn-, (Z)- or suprafacial] of the reacting double bond. However, it is usually desirable to avoid stoichiometric concentrations of expensive, heavy metal poisons. Therefore, the observation that catalytic quantities of osmium(Vni) tetroxide (OSO4) could effectively be used in the presence of a less noxious oxidizing agent (the N-oxide of N-methylmorpholine, NMO) was particularly important. The function of the latter then is to convert the osmium(VI) trioxide (OsOs), produced when the osmium(VIII) tetroxide is reduced (as it performs the oxidation), back to osmiiun(Vni) tetroxide (OSO4), that is,... 

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