Tropones, reactions with

The addition of benzonitrile oxide to cyclooctatetraene produced a monoadduct which was induced to undergo valence tautomerism to produce a tricycloisoxazoline (Scheme 104). A similar reaction with tropone gave a minimum of eight adducts from which two monoadducts were isolated (Scheme 104) (70T5113). 

This series is punctuated by several unusual synthons, one the reaction of tropone (567) with aniline to give (568). The cyclization of (569) with sodium hydroxide gave (570) (67AHC(8)277, 69M602). The reaction of in situ generated benzyne with the nitrone (571) produced (572) (67AHC(8)277). 

Tropolone has been made from 1,2-cycloheptanedione by bromination and reduction, and by reaction with A -bromosuccinimide from cyolo-heptanone by bromination, hydrolysis, and reduction from diethyl pimelate by acyloin condensation and bromination from cyclo-heptatriene by permanganate oxidation from 3,5-dihydroxybenzoic acid by a multistep synthesis from 2,3-dimethoxybenzoic acid by a multistep synthesis from tropone by chlorination and hydrolysis, by amination with hydrazine and hydrolysis, or by photooxidation followed by reduction with thiourea from cyclopentadiene and tetra-fluoroethylene and from cyclopentadiene and dichloroketene. - ... 

Ai -A-homo-4-ketones by reaction with lithium and biphenyl at The resulting dienone is transformed into the corresponding tropone by treatment with bromine. The Swiss chemists also found that base treatment of 19-mesyloxy-A " -3-oximes gives directly 4-oximino-A-homo-estra-l(10),2,4a-trienes in moderate yield. ... 

The study of high pressure cycloaddition reactions of tropone (125) with maleic anhydride and norbornene allowed the reaction activation volumes to be measured and showed that they are large, negative and solvent-dependent (Scheme 5.17) [43a]. 

All the bridged [1 ljannulenones condense with malondinitrile in acetic anhydride and yield the corresponding dicyanomethanohendecafulvenes (e.g. 11 - 38) and these on treatment with strong acid furnish the substituted l,6-methano[ll]an-nulenium ions. 11 -Chloro-3,8-methano[ 11 Jannulenone 31, in parallel with the behaviour of the similarly 2-substituted tropone, undergoes reaction with sodium meth-oxide at room temperature to afford chiefly the products of normal 39 and cine substitution 40. 

Machiguchi, Nozoe and coworkers have very recently observed that in contrast to chemical reactivity of tropones, the tosylate of tropone oxime undergoes a facile ring-opening to 6-substituted (Z,Z,Z)-1,3,5-hexatriene nitriles on reaction with various nucleophiles305. For example, reaction of phenyl lithium results in the corresponding hexatriene carbonitrile (equation 183). 

Mahon and colleagues297 studied the cycloaddition reactions of substituted cis-1,2-isopropylidenedioxycyclohexadienes. The reaction of tropone (471) with cyclohexadiene 472, for example, afforded the expected exo cycloadduct 473 with good yield (equation 140). 

Rigby and coworkers305,309 also performed metal mediated [6 + 4] cycloadditions of heterocyclic trienes and tropones with various dienes. In concurrence with the all-carbon trienes, the electronic nature of the diene partners generally had little influence on the cycloaddition efficiency. The only reported exceptions are the reactions of thiepin-1,1-dioxides. Lower yields were observed in the reactions involving electron-deficient dienes in comparison with the reactions with electron-rich dienes. The reaction of complex 514... 

The tropone ring of cyclohepta[c]thiophen-6-one reacts preferentially at the C=C bond, instead of at the carbonyl group, with both dichloro- and dibromocarbene to give mono- and bis-adducts in relatively low yields (5-40%) [60]. Benzoquinones produce anfi-bis-insertion adducts in their reaction with chloroform (95%), or bromoform (57%), under basic conditions [29]. 

Reactions of tropone 124 with phenylacetonitrile (62YZ892) and transformations of type 124 derivatives by several active methylene compounds (63MI2) result in rearrangements to form 8-quinolinol derivatives. (Thia-zolo[4,5-i)]tropones prepared from 124 will be treated in Section II,B,l,f.)... 

Access to alkyl substituted derivatives of the homotropylidene complexes is provided via the >j4-tropone iron complex by reaction with diazoalkanes, followed by mild thermolysis of the 3+2 py razoline adduct to give the corresponding homotropone complexes (equation 149)217,218. The 8,8-dimethyl derivative was used as starting material for the preparation of the fluxional ( 5-2,8,8-trimethylbicyclo[5.1.0]octa-2,4-dienylium)Fe(CO)3 cation complex219. More recently (homotropone)Fe(CO)3 was used for the synthesis of unique chiral 1,2-homoheptafulvene iron complexes220 221. 

A secondary orbital interaction has been used to explain other puzzling features of selectivity, but, like frontier orbital theory itself, it has not stood the test of higher levels of theoretical investigation. Although still much cited, it does not appear to be the whole story, yet it remains the only simple explanation. It works for several other cycloadditions too, with the cyclopentadiene+tropone reaction favouring the extended transition structure 2.106 because the frontier orbitals have a repulsive interaction (wavy lines) between C-3, C-4, C-5 and C-6 on the tropone and C-2 and C-3 on the diene in the compressed transition structure 3.55. Similarly, the allyl anion+alkene interaction 3.56 is a model for a 1,3-dipolar cycloaddition, which has no secondary orbital interaction between the HOMO of the anion, with a node on C-2, and the LUMO of the dipolarophile, and only has a favourable interaction between the LUMO of the anion and the HOMO of the dipolarophile 3.57, which might explain the low level or absence of endo selectivity that dipolar cycloadditions show. 

Eschenmoser s pyrone 38 on treatment with cyclopropenone ketal 39 in refluxing benzene afforded lactone 40 (73%). Lactone 40 on hydrolysis with acetic acid at 100°C afforded, after deprotection and decarboxylation, tropone 37 (70%). Introduction of the tropolonic hydroxyl group was achieved with hydrazine hydrate in ethanol, to give a mixture of deacetyl-colchiceinamides 41 (53%) and 42 (37%), followed by reaction with ethano-lic potassium hydroxide, which afforded tropolones 43 and 44, respectively. Tropolone 43 was converted to 44 which, therefore, became the major reaction product. Methylation of 44 gave a mixture of enol ether 18 and 45 which were separated by chromatography. 

Finally, during the reactions with one to three molar equivalents of benzyl chloride, pyrrole 435 was attacked at C-3 and at its nitrogen and tropone oxygen atoms (65CPB473) mono- (436), di- (437a,b), and tribenzyl derivatives (438a,b) were isolated (Scheme 118). 

Deprotection of a dimethyl acetal at a late stage in a synthesis of the unusual diterpenoid tropone Hainanolido was not a problem.123 What was a problem was the fate of the aldehyde released because under most conditions, the aide-hyde underwent a very easy Prins-like reaction with the cycloheptatriene ring to give the tetracyclic product 573 [Scheme 2.57], This reaction could not be suppressed completely, but it was minimised by using zinc bromide to deprotect the dimethyl acetal 57.1. The desired aldehyde 573 was obtained in 61 % yield together with 16% of the unwanted 573. 

Tropones 2,4.6-Trimethylphenol (l)reacts withdichloro-ordibromocarbcne(halo-genoform and phase-transfer catalyst) to provide the dienones 2 and 3, which on reaction with Bu,SnH are both converted into 2,4,7-trimethyltropone (4). 

The thermally induced [6 + 4] cycloaddition of 2,4,6-cycloheptatrien-l-one (tropone) (1) with a variety of diene pikers has played a central role in the development of the mechanistic precepts and preparative utility of the entire class of higher-order pericyclic processes. The relatively well-defined reaction parameters for these cycloadditions render diem particularly well-suited for the rqiid assembly of relatively complex polycyclic carbon arrays. 

The initial disclosure of a [6 + 4] cycloaddition between tropone (1) and a 1,3-dipole involved diphe-nylnitrilimine as depicted in Scheme In this instance the [6 + 4] pathway competed rather poorly with various alternative [4 + 2] pathways and only a small quantity of the adduct in which the dipole added across the 2- and 7-positions of (1) was recovered. The three [4 + 2] adducts (45)-(d7) that were isolated from the reaction mixture presumably arose from a base-catdyzed hydrogen shift that occurred subsequent to the initial cycloaddition. Efforts to account for the divergent behavior of dienes and 1,3-dipolar species in their reactions with tropone have included invoking a dipole repulsion between the large positive charge located on the central atom of the 1,3-dipole and the partial positive charge on tropone, which must come into close proximity in the transition state of a concerted [6 + 4] cycloaddition. A ca-... 

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