Ring expansion, of aromatic

Ring expansion of aromatic compounds by carbene, carbethoxycarbene, chlorocarbene, and carbenoid is well known 256, 336, 351-356). Muller and co-workers reported the reaction of aromatic compounds with carbene generated from a catalytic decomposition of diazomethane with copper salts, and proposed a bimolecular two-step mechanism involving an inverse ylid for the reaction. Miller (336) proposed another bimolecular two-step mechanism for the reaction of benzene with alkylcarbenoids of aluminum. Baldwin and Smith (25) proposed a concerted mechanism for the reaction of aromatic compounds with carbethoxycarbene. Reaction of alkylbenzene with diethylzinc and ethylidene iodide gives 7-methylcyclohepta-l,3,5-triene derivatives in yield 369). The... 

The formation of norcaradiene derivatives with naphthalene [reaction (22)] lends some support to this scheme. This mechanism resembles a bimolecular two-step process suggested for the reaction of chloromethyl-aluminum compounds with olefins (199-201). On the other hand, a bimolecular one-step methylene transfer mechanism is generally accepted for the formation of cyclopropane derivatives by the reaction of halo-methylzinc compounds with olefins. This difference between the mechanism proposed for the cyclopropane formation from olefin and that for the ring expansion of aromatic compound may be ascribable to the difference in the stability of intermediates the benzenium ion (XXII) may be more stable than an alkylcarbonium ion (369). 

The ring expansion of aromatic azides, long established as a preparative procedure for azepines, has been applied to the formation of benzo-2,4-diazepines. Photolysis of 4-isoquinolyl azides in the... 

Reactions of Thioacetals. The ring expansion of aromatic thioacetals can be achieved using NBS initial bromination a to the thioacetal is followed by ring expansion and proton transfer... 

The cyclopropane derivative 1, formed by the addition of dibromocarbene to 4-ethoxy-l-tosyl-1,2-dihydroquinoline, in refluxing pyridine undergoes ring expansion and aromatization to the 1/f-l-benzazepine 2.168... 

Fluorinated dihalocarbenes have been used as central synthons in the synthesis of fluorinated aromatics from cyclopentadienes.62 The reaction proceeds via a fluorinated fused bicyclic cyclopropane, which upon heating undergoes a ring opening to achieve the ring expansion of the second cycle. 

Reaction of cyclopropenes with cyclopropenium ions leads to a three carbon ring expansion to aromatic derivatives, presumably through ring opening of an initially formed cyclopropenyl-cyclopropylcation 276) ... 

A palladium-catalyzed three-component reaction with 2-iodobenzoyl chloride or methyl 2-iodobenzoate, allene and primary aliphatic or aromatic amines to prepare fV-substituted 4-methylene-3,4-dihydro-1 (27/)-isoquinolin-1 -ones was disclosed <02TL2601>. A synthesis of 1-substituted 1,2,3,4-tetrahydroisoquinolines via a Cp2TiMe2-catalyzed, intramolecular hydroamination/cyclization of aminoalkynes was also reported <02TL3715>. Additionally, a palladium-catalyzed one-atom ring expansion of methoxyl allenyl compounds 79 to prepare compounds 80 that can serve as precursors to isoquinolones was reported <02OL455,02SL480>. 

The cyclobutanone ring in the ether 7, derived by ring expansion of an oxaspiropentane, intramolecularly alkylates the activated aromatic system on treatment with PTSA, leading to 2W-cyclobuta[c]chroman-4-ols 8 (X = OH). Subsequent fission of the four-membered ring yields 3,4-disubstituted 2//-chromenes <02SL796>. A variation of this approach allows the synthesis of the 4P-phenylsulfanyl derivative of 8 (X = SPh), oxidation of which affords the cyclopropa[c]chroman entity <02OL2565>. 

Hydrolytic cleavage of the C-O bond of bicyclic, tetracyclic, and steroidal enolates with HF-SbFs induces their isomerization to the corresponding ketones (Scheme 14.41) [104]. Rearrangement of dienones to aromatic compounds is also promoted by HF-SbFs (Scheme 14.42) [105]. Ring expansion of methyl penicilli-nates is achieved by SbCls to give thiazepine derivatives [106]. 1,3-Dithianes derived from ketones and aldehydes are deprotected with SbCls by means of a single-electron-transfer mechanism [107]. 

The fungal tropolones puberulic acid (4.29) and stipitatic acid (4.30) were isolated from P. puberulum and P. stipitatum by Raistrick in 1932 and 1942, respectively. Their structures were not established at that time despite extensive chemical degradation. The tropolone structure for stipitatic acid was proposed by Dewar in 1945 and that for puberulic acid in 1950 by Todd. These structural proposals played an important part in the development of ideas of aromaticity. The biosynthesis of these tropolones involves the ring expansion of an orsellinie aeid via stipitatonic acid (4.31). 

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