Tropone, synthesis

Birch s procedure for tropone synthesis appears to be widely applicable to 2,3- or 2,5-dihydroanisole derivatives which are readily obtained by reduction of appropriate aromatic methyl ethers by alcoholic metal-ammonia solutions. " Additional functional groups reactive to dibromocarbene or sensitive to base such as double bonds, ketones and esters would need to be protected or introduced subsequent to the expansion steps. 

In yet another tropone synthesis Skattebol has shown that dibromocyclopropanes carrying a phenolether function react to 1 l-oxa-tricyclo[5.5.0.07,9]undecatrienes when treated with methyllithium. The strained polycyclic intermediate is converted into a 2-alkenyltropone derivative when heated to about 200 °C [137]. 

This tropone synthesis was used for a short synthesis of nezukonc (7) (equation 1). 

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. - ... 

An ingenious approach to the synthesis of steroids incorporating a tropone A ring has been developed by Birch and co-workers. Addition of dibromocarbene to 3-methoxyestra-2,5(10)-dien-17-one 17-ethylene ketal (42) gives a monodibromocarbene adduct formulated as (43) accompanied by a minor amount of a bisadduct. This confirms earlier observations that electrophilic halocarbenes add mainly to 2,3- or 2,5-dihydroanisoles at the double bond bearing the methoxyl group. 

Synthesis of tropones, tropolones, and tropylium salts with fused heterocyclic rings 95AHC(64)81. 

Another versatile two-step synthesis of homobarrelenones [45] is based on the high pressure cycloaddition of tropone (125) and its 2-methoxy-, 2-hydroxy- and 2-chloro-derivatives with 2,3-bis(methoxycarbonyl)-7-oxabicyclo[2.2. l]hepta 2,5-diene (133) followed by thermolysis of the cycloadducts at 130 °C with the... 

Similarly, a number of 2-(2-arylhydrazino) tropones undergo the benzidine rearrangement when treated with HC1 in EtOH to give 2-amino-5-(4-aminoaryl)tropones, which can be hydrolysed to the corresponding 5-aryl-tropolones. This is a useful route to a synthesis for open B ring colchine analogues25. 

These transformations were applied to develop a new promising method for synthesis of various bridged polycyclic systems66, viz. ketones 160 and 161. Tropone reacts with butenyl magnesium bromide (—78 °C, 75%) to form a mixture of 2-(3-butenyl)dihydrotropones 158 and 159, the pyrolysis of which (200-210 °C, neat or in heptane solution) leads to 60% total yield of the isomeric homoprotoadamantenones 160 and 161 and the tricyclic ketone 162 in a ratio of 58 18 24, respectively (equation 49)66. 

Tropones, Tropolones, and Tropylium Salts with Fused Heterocyclic Rings Part I Synthesis ... 

Gronowitz and co-workers prepared dithieno[6,6 ]tropones by cycli-zation of pure (Z)-l,2-dithienylethenecarboxylic acids via acid chlorides in the presence of SnCU [73CS(3)165]. The corresponding synthesis of... 

This reaction is applicable to a dithienotropone synthesis starting from tropone 2,7-bis(thioether). An earlier attempt at rearrangement of 2-(allylthio)tropone with xylene as solvent failed (59MI2). 

Furthermore, the homologous complex 286 condenses with ethyl orthoformate to give, in the course of a new y-tropolone synthesis, tropolone ether 287 by O-ethylation it is transformed to tropylium salt 288 (Scheme 72 70JA6382) the corresponding tropone complex was synthesized from dibenzotroporic and Cr (CO)6 [83AG(S)734]. 

The synthesis of tropones, tropolones, and tropylium salts with fused heterocyclic rings forms the first part of a projected two-chapter sequence by G. Fischer (Leipzig, Germany). It is planned that the structure, reactivity, and applications of these compounds will be discussed in a further contribution in a subsequent volume. 

Oxygenated dienes are exceptional substrates for vinylcarbenoids [78]. In order to avoid side-products derived from zwitterionic intermediates, nonpolar solvents are typically employed. A short synthesis of nezukone 57 highhghts the utiHty of the [3-1-4] cycloaddition for the synthesis of tropones (Scheme 14.4). The cycloaddition between the oxygenated butadiene 55 and 52 generates the cycloheptadiene 56 in 67% yield [78]. Treatment of 56 with Meli followed by acid-induced dehydration completes a very short synthesis of nezukone 57. 

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