Acetophenones, substituted, nature

While it has been assumed (Galardy et al., 1973) that the reactive species is the mr excited state this may not always be the case. For acetophenones the nature of the photogenerated triplet is highly solvent dependent (Turro, 1979). In more polar environments the species formed is the jot state which is less reactive than the mr state and in certain cases it may prove useful to substitute the molecule with an electron withdrawing group (e.g. CFr) on the aromatic ring to ensure formation of the desired T, (mt ) intermediate. 

Low-potential electron-transfer mediators such as viologens can substitute natural cofactors (particularly NADH) in some enzymatic reactions [184], The electrochemical reduction of viologens has been studied extensively [185] and they and other reductive electron mediators have been utilized to drive enzyme-catalyzed reactions [186], For instance, the electrochemical reduction of NAD(P)+ to NAD(P)H with a current efficiency of more than 97 % was achieved using alcohol dehydrogenase in the presence of acetophenone as an electron mediator [187], The addition of acetone or acetaldehyde as a substrate to the above bioelectrocatalytic system allowed the reduction of the substrate to the corresponding alcohol at alcohol dehydrogenase accompanied by the oxidation of the resulting NAD(P)H. 

The response of the peroxybenzoates to the CIEEL activators depends remarkably on the nature of the substituent. The unsubstituted peroxybenzoate [29a] behaves in a fashion nearly identical to that observed for the peroxyacetate [28]. The p-methoxy-substituted peroxybenzoate [29b] behaves quite like the parent, but the nitro-substituted compounds [29d] and [29e] and the p-dimethylamino-substituted peroxybenzoate [29c] behave quite differently. The properties of these compounds, however, can be understood within the CIEEL mechanism. For example, the nitro-substituted peroxybenzoates [29d] and [29e] with DMAC exhibit a value of k2 approximately ten times greater than for the unsubstituted peroxide. Yet the yield of excited singlet DMAC generated by [29d] and [29e] is 700 times less than from 29a. This seeming inconsistency can be easily understood. In the postulated CIEEL path, the reduction of the peroxide results in its fragmentation to acetophenone and an acid. One of these species must be a radical anion. For the peroxyacetate and all of the substituted peroxybenzoates examined, with the exception of the nitro-substituted examples, the more easily reduced species of this pair is... 

Yen and co-workers [54] have reported an efficient one-pot procedure for the synthesis of 4,6-diaryl-2-pyridinones 3 based on a cyclocondensation reaction of iV-ethoxycarbonyl-methylpyridinium chloride or iV-carbamoylmethyl p3Tidinium chloride with an aromatic aldehyde and a substituted acetophenone. The MCR was performed under microwave irradiation (domestic oven) with NTUOAc/AcOH as the reaction medium. The nature of the substituents on the aromatic aldehyde and ketone seem to have little influence on the obtained yields. The highlights of this approach include a convenient and simple experimental procedure with easy product isolation (Scheme 3). 

The following discussion will be focused on the effect of structural variations on the kinetics of fragmentation, the cleavage mode, and the stepwise or concerted nature of the process. Similar concepts have also been applied to the reductive cleavage reactions of other series of substrates, i.e. a-substituted acetophenones [246-250], perbenzoates [240, 251], peroxides [242, 252-256], sulfides [244, 257, 258], sulfonium salts [259-263], nitrocumenes [264, 265], arylmethyl aryl ethers and thioethers [266-270]. 

A one-step synthesis was achieved using the natural zeolite E4 (clinoptilolile type) modified towards a more acidic form E4a. Reactants studied include b-phenylethylamine and its 3,4-dimethoxy-dcrivative and substituted acetophenones as well as a series of bcnzaldehydes [90]... 

The reaction of 4-bromobenzaldehyde with substituted acetophenones and urea gave aryl-substituted pyrimidin-2-ones 63 or hexahydro-l//,8//-pyrimido[4,5-rfJpyrimidin-2,7-diones 64, depending on the nature of the acetophenone substituent and the solvent <04CHE194>. Two new approaches to 2,4-dialkylamino-substituted 6,7-dihydro-5//-benzocyclohepta[l,2-c( pyrimidines were developed, one based on the reaction of substituted cyanamides and the enol triflate of 1-benzosuberone, and the other based on nucleophilic displacements at C2 and C4 of... 

Knoevenagel condensation under focused MWI for 1-7 min of 2-hydroxy or 2-methoxy-substituted benzaldehydes or acetophenones 99 and Meldrum s acid (100) using a solid catalyst combination of natural kaolinitic clay or Envirocats (EPZG, EPZIO) gave 3-carboxycoumarins 101 in 55-97% yields (Scheme 20) (99MI4). 

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