The Concept of Multicatalysis in Aerobic Oxidation of Alcohols - Transition Metal Catalysis in Aerobic Alcohol Oxidation - page 187

Ph OH

PI/CB-Au/Co (2 mol %)
NaOH (2 equiv)

34

O

+

(7.8)

Ph N

H

CO 2 H

THF/H 2 O 9:1
O 2 (1 atm), 25 °C, 12 h

36 , 72%

H 2 N

2 H

35

The direct lactamization of amino alcohols catalyzed by PI-CB/Au-Co
has also been reported. This strategy is particularly effective for the synthesis
of isoindolin-1-one and 3,4-dihydroisoquinolin-1(2H)-one ring systems
(Equation 7.9). 29

PI/CB-Au/Co (5 mol %)
NaOH (1 equiv)

O

OH

NH

(7.9)

THF/H 2 O 19:1
O 2 (1 atm), RT, 24 h

NH 2

37 38 , 82%

7.4 Catalytic Aerobic Oxidation of Alcohols
in Multistep Processes
As mentioned in the last section, catalytic multistep reactions can be an
elegant tool to build molecular complexity in a single vessel without puri-
fication of intermediates. This section describes multicatalytic processes in
which two or more catalysts execute different chemical reactions in tandem
or sequentially. Some examples of multicatalysis take advantage of the ver-
satile properties of a transition metal to promote more ecient mono-
catalytic multistep reactions. In all cases, at least one stage is a catalytic
aerobic oxidation step. Only examples in which two or more distinct catalytic
cycles are achieved in a single vessel will be presented here. 30
Lebel and Paquet reported the combination of a palladium and a rhodium
catalyst for the olefination of alcohols. 31 Alcohols were treated with a pal-
ladium catalyst 39 (which was known to catalyze aerobic oxidation) 32 under
an atmosphere of oxygen to produce the corresponding carbonyl derivative.
These carbonyl intermediates were further reacted in the same vessel under
Wilkinson's catalyst methylenation reaction conditions, affording terminal
alkenes in good to excellent yields (Table 7.4). Up to four individual transfor-
mations can be achieved starting with the diol substrate 53 (Table 7.4, entry 7).
In the same study, an intramolecular tandem methylenation-ring closing
metathesis was accomplished using the metathesis catalyst 55 developed by
Nolan's group. 33 Lebel and Paquet demonstrated that both multicatalytic
oxidation-methylenation and methylenation-ring closing metathesis can be
combined in the same vessel (Equation 7.10). This reaction provided an
impressive example of catalyst compatibility as the three different transition
metal catalysts coexisted and did not interfere in the reaction mixture.