Naphthoquinones Nitrates

Amines can also be protected by this reagent cleavage must be carried c acidic media to avoid amine oxidation. The byproduct naphthoquinone can 1 moved by extraction with basic hydrosulfite. Ceric ammonium nitrate also s as an oxidant for deprotection, but the yields are much lower. 

Furoquinones, such as naphtho[2,3-b]fiiran-4,9-dione, naphtho[l,2-b]fiiran-4,5-dione, benzofuran-4,7-dione and benzofiiran-4,5-dione derivatives are available by the ceric ammonium nitrate mediated [3+2] cycloaddition of 2-hydroxy-1,4-naphthoquinones and 2-hydroxy-1,4-benzoquinones with alkenes or phenylacetylene <96CL451>. 

A solution of sodium nitrate (0.69 g, 10 mmol) in water (5 ml) was added at 0-5°C to a solution of 6-amino-2,3-dimethoxy-l,4-naphthoquinone (1.17 g, 5 mmol) in 5 1 acetic acid water (25 ml) containing concentrated hydrochloric acid (1.7 ml). A further quantity of sodium nitrite (0.69 g) was then added to the reaction mixture after cooling to -5°C, followed by a solution of cuprous chloride (0.6 g) in concentrated hydrochloric acid (5 ml). The mixture was allowed to warm to room temperature and solid cuprous chloride was added portionwise until the mixture assumed a green color. Water was then added to the reaction mixture and the precipitated yellow solid filtered off, washed with water and recrystallized from methanol water (2 1) giving 1.01 g of 6-chloro-2,3-dimethoxy-l,4-naphthoquinone, melting point 93-94°C (from ether-petrolium ether). 

Treatment of 2-amino-1,4-naphthoquinone (133) and acetylacetone with Mn(OAc)3 generates an oxidatively condensed alkaloid (134) (eq. 4.46b). The same oxidative reaction of 2-amino-1,4-naphthoquinone (135) and (3-diketone with cerium(IY) ammonium nitrate (CAN) can be performed (eq. 4.47). 

The synthesis of quinones from arenes is an area which demands further research, despite the number of reagents presently available for this transformation. This is highlighted by the synthesis of the naphthoquinone (3). Direct oxidation of the dibromoarene (1) was unsatisfactory, and therefore Bruce and coworkers had to resort to a multistep sequence involving nitration, reduction, diazotization, displacement by hydroxide and finally oxidation of the phenol (2) with Fremy s salt (Scheme 1). Although there are examples of the oxidation of polynuclear aromatic hydrocarbons to quinones, the direct oxidation of an arene to a quinone is a process not encountered in the synthesis of more complex mt ecules. 

The oxidation of naphthols to 1,4-naphthoquinones is accomplished by ceric ammonium nitrate (equation 315) [423]. 

Cerium(IV) presents an interesting case. The useful oxidant ceric ammonium nitrate (CAN) can be extracted from an aqueous solution as a complex salt [NBu4]2[Ce(N03)6] into hexane. Ceric ammonium sulfate, however, being a true double salt, cannot be transferred by a QX catalyst [14], In an actual catalytic oxidation procedure, naphthalene is converted into naphthoquinone in a water/hexane... 

The most important application of CAS is in the oxidation of aromatic rings. CAN oxidizes polycyclic aromatic hydrocarbons only in moderate yields (20-60%), and these reactions are often complicated by the formation of nitrate esters. In contrast, CAS generally oxidizes aromatic hydrocarbons to quinones in good yields. For example, naphthalene is oxidized to 1,4-naphthoquinone in excellent yield by CAS in a dilute mixture of H2SO4 andMeCN(eq 1). ... 

Diverse dihydronaphtho[l,2-(r]furans were generated fix)m 1,4-naphthoquinones and olefins in the presence of ceric ammonium nitrate (13OBC6097). ( )-Lantalucratins A and B were produced in the presence of diammonium cerium(IV) nitrate (13T10470).Benzo[(>]furan moieties were synthesized by a three-component Mannich reaction of 3-acetyl-2H-chromen-2-one or l-(l-benzo[fc]fioran-2-yl) ethanone with p-substituted aromatic aldehydes and aromatic amines with ceric ammonium nitrate (CAN) as a catalyst (13MCR4787).p-Alkenylphenols went through the oxidative dimerization to generate substituted dihydrobenzo[l)]furans in the presence of CAN (13T653). 

Mononitration of 1-hydroxynaphthalene could be obtained by use of ammonium hexanitra-tocerate(IV) supported on silica gel in acetonitrile (Chawla and Mittal, 1985) (scheme 39). The same reaction with CAN in acetic acid give the 2,4- and 4,6-dinitro derivatives. By the same method, 2-hydroxy naphthalene is converted into l-nitro-2-hydroxy naphthalene and 4-nitro-2-hydroxynaphthalene (scheme 40). The 1-alkoxynaphthalenes can be mononitrated regioselectively in the 4-position (scheme 41). The lower reactivity of CAN supported on silica gel is also evident from the fact that naphthalene derivatives are not oxidized into 1,4-naphthoquinones. The authors noticed that no reaction could be observed when ammonium hexanitratocerate(IV) was replaced by a mixture of ammonium nitrate and ammonium cerium(IV) nitrate. Silica supported CAN has also been used for the nitration of methoxyben-zenes (Grenier et al., 1999) and less electron rich aromatic compounds like benzene, toluene, chlorobenzene and bromobenzene (Mellor et al., 2000) (scheme 42). For the less electron rich aromatics, dichloromethane is used as solvent instead of acetonitrile. In most cases, the yields are good to excellent. 

Similar to urea, thiourea also gives a reaction with p-dimethylaminobenzal-dehyde (p. 322), it is precipitated with xanthydrol (p. 272), and is reduced with ammoniacal silver nitrate (p. 210). On reaction with monochloroacetic acid it is changed to rhodanin, which can be detected with sodium 1,2-naphthoquinone-4-sulfonate (16). 

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