Aromatic rings without carbonyl groups

Structure of Five-membered Rings with Two or More Heteroatoms 

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It should be noted that if the non-phenolic Ca-carbonyl compound contains an aromatic ring without Ca-carbonyl group (i.e., the structure should contain at least two aromatic rings), then the compound will be a substrate for lignin peroxidase and will be degraded according to the mechanisms discussed above. Degradation of this type of compounds can result, for example, in the formation of vanillin and vanillic acid derivatives (see compounds 7a and 8). As has been shown by Eriksson and coworkers... 

The styrene double bond in 9(ll)-dehydroestradiol 3-methyI ether (1) or its 8-dehydro counterpart is reduced by potassium or lithium in ammonia without affecting the aromatic ring estradiol 3-methyl ether (2) is formed from both compounds. Reduction of the corresponding 17-ketones occurs with partial or complete reduction of the carbonyl group. Lithium... 

The inertness of ordinary double bonds toward metallie hydrides is quite useful, since it permits reduction of, say, a carbonyl or nitro group, without disturbing a double bond in the same molecule (see Chapter 19 for a discussion of selectivity in reduction reactions). Sodium in liquid ammonia also does not reduce ordinary double bonds, although it does reduce alkynes, allenes, conjugated dienes, and aromatic rings (15-14). 

The 1,4-addition reaction of unsaturated carbonyl compounds with Ph3Bi smoothly proceeded in the presence of rhodium catalysts (Scheme 54) [67,68]. Interestingly, the reaction can be conducted in a H20/THF mixture under air. Methyl cinnamate, having an OH group on the aromatic ring, was efficiently phenylated without the protection of the OH group. 

In aryl alkyl ketones, there are two types of C-F bonds to reduce. Fluorine atoms in the a-positions are usually more easily replaced than those on the aromatic ring. It is also possible to reduce a-C-F bonds selectively without affecting the carbonyl group. 

In (C5Me5)Rh(C2H3SiMe3)2-catalyzed C-H/olefin coupling the effect of the coordination of the ketone carbonyl is different from that in the ruthenium-catalyzed reaction [10], In the rhodium-catalyzed reaction all C-H bonds on the aromatic ring are cleaved by the rhodium complex without coordination of the ketone carbonyl. Thus, C-H bond cleavage and addition of Rh-H to olefins proceed without coordination of the ketone carbonyl. After addition of the Rh-H species to the olefin, a coordinatively unsaturated Rh(aryl) (alkyl) species should be formed. Coordination of the ketone carbonyl group to the vacant site on the rhodium atom leads... 

Structurally similar polymers with azo links, Polymers 9 and 10, formed no meso-phases when the rigid aromatic unit contained terminal carbonyl groups, but these formed nematic mesophases when the ester link was reversed The transition temperatures of the azo and azoxy polymers with the same spacer were quite close to each other. Substitution of methyl groups on the phenylene rings of these polymers reduced melting temperatures without adversely affecting nematic mesophase stability... 

Energetic reduction with lithium aluminum hydride led to the reduction of the carbonyl group with the formation of the correct alcohol epimer, as expected from the steric hindrance presented by the benzene ring, and to removal of the aromatic bromine. This last reaction is a noteworthy example of the removal of aromatically bound halogen without reduction of either an allyhc hydroxyl or a double bond. The codeine so produced (CCCLXXXIII) was then demethylated to morphine (CCCLXXXIV) by short heating to 220° with pyridine hydrochloride. 

Hydrogenation will remove even a conjugated double bond without affecting the carbonyl group (Chapter 14) or an aromatic ring. 

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