Aminotropones

Aminotropones have been reported through a single-step cyclization-ring expansion process from 4-aminocyclohexa-2,5-dienones (p-quinamines) bearing a 4-sulfinyl or 4-sulfonyl methyl group on reaction with sodium hydride (Scheme 62).97... 

The 4-hydroxypyridine (or 4-pyridone) derivatives are obtained by the use of ethoxymethylenemalonate and acetoacetate (59NKZ534) or acetylenedicarboxylate (78USP4130649). In analogy to these reactions, cyclizations starting from 5-aminotropolone ethers (83USP4382088) or 2-aminotropones (83USP4381304) were claimed. 

The reactions of tropone with hydroxylamine or hydrazine yield 2-aminotropone (59MI1, p. 415), in the first case admixed with troponeoxime (Section IV,A,8,b). Besides nucleophilic substitution, an additive mechanism was discussed (66MI2, p. 135 73CRV293, p. 354). 

Amidation of anhydrosepedonin dimethyl ethers (418b,c) by liquid ammonia leads to isomeric 2-aminotropones like 422b (69MI3). 

Tropon-2-ylimino)triphenylstibane, prepared by the Kirsanov reaction between Ph3SbCl2 and 2-aminotropone, undergoes a formal [8+ 2]-type electrocyclization with carbon disulfide, phenyl isocyanate, phenyl isothiocyanate, and diphenylcarbodiimide to give the corresponding cyclized products in moderate yields (Equation (35)).68... 

Although in some cases, copper catalysis has little effect on the stereochemistry, some asymmetric induction by chiral copper catalysts such as copper(i) complexes of aminotropone iminates (8) [79] or the chiral arylthiocopper compound (9) [80] has been achieved. Chiral zinc(n) complexes (8) also promote enantioselective conjugate addition [81]. 

J. F. Liebman and R. M. Pollack, in The Chemistry of Enones (Eds. S. Patai and Z. Rappoport), Wiley, Chichester, 1989. Buried enones in this chapter included pyrrole-2-aldehyde, 4-pyridone, 2-aminotropone, p-dimethylaminobenzaldehyde, indigotin and both methylphaeo-phorbide a and b. These compounds may also be recognized as buried enamines. 

Nickel carbonyl reacts with o-quinoneimine with displacement of all the carbonyl groups to form Ni(N2C H4)2 (XCII) 41), and Fe(CO)5 reacted with aminotropone imines to form (XCIII R = Me, Et, Ph, p-MeC6H4). 

Lippard and co-workers [33] reported the same addition, but catalyzed by copperl(I) complexes with bidentate chiral auxiliary ligands (see Table 4, entry 2). The products, as precursors to prostaglandin synthesis, were formed in moderate yield and low e.e. when Cu(R-CHIRAMT), a chiral aminotropone imine, was used. However, higher enantiomeric excess purities (> 70%) were obtained when a silyl reagent and hexamethylphosphoramide (HMPA) were added. Not surprisingly, both catalysts gave similar products with similar enantiomeric purities. 

The [4-1-3] cycloaddition between 2-aminofuran and oxyallyl cations, followed by base-induced elimination of the resulting adducts, was used in the synthesis of 3-aminotropones <05TL8475>. A chiral Lewis acid-catalyzed [4t-3] cycloaddition between furans and nitrogen-stabilized oxyallyl cations derived from allenamides was developed. As depicted below, the Cj-symmetric salen-based ligand is the most effective in promoting this asymmetric cycloaddition reaction <05JA50>. 

We thus conclude that tropolone has a greater degree of stabilization than 2-aminotropone, a rather surprising conclusion perhaps, until it is realized that esters (and thus presumably carboxylic acids) have higher resonance energies than amides . 

Dulaaia guignensisA new a-aminotropone, manicoline A (37), has been isolated from the root bark of this tree. ... 

The most important and thoroughly examined examples of square-tetrahedral equilibria are provided by the JV-(.yec-aIkyl)salicylaldiminato complexes and the aminotropone iminato complexes (25-G-X).11 In the tetra-... 

Reactions with Nucleophiles. As an enone tropone is readily susceptible to attack by nucleophiles in Michael-type reactions which might take place at any site in the ring. An early reported example was the formation of 2-aminotropone by reaction with either hydrazine or hydroxyl amine [169]. Reaction olsviously proceeds by conjugate attack (preferred over attack at the carbonyl group) followed by elimination of water or ammonia ... 

Closely related to these reactions with nucleophiles are those of aminotropones with nitrous acid. Thus from 2-amino-4-methyl-tropone and 2-amino-6-methyltropone no diazonium compound could be detected and the products were a mixture of m-toluic acid and either 2-hydroxy-6-methyl- or 2-hydroxy-4-methyl-benzaldehyde [206]. 

Alkoxytropones [230] and some aminotropones [231] are converted into bicyclo[3 2 0]compounds on photolysis. Two alternative types of product may be formed and further rearrangements may follow, e.g. 

Both reagents react with 3-dimethylaminotropone exclusively at the oxygen atom [338]. 3-Aminotropone is acetylated at nitrogen with bromine it gives a monobromo derivative [339]. 

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