Oxidation spirodienones

The electrochemical oxidation of 4-(2 -alkenylphenyl)phenols (32) in MeCN/ MeOH affords spirodienones (33) arising from cyclization by the intramolecular addition of the 4-position of the phenol to the olefinic side chain and... 

Intramolecular oxidative coupling of silylated phenols 251 with IBTA leads to the formation of spiropiperidine derivatives 253, called aza-anthraquinone-spirodienones (89TL1119) (Scheme 64). The first step of this conversion is the electrophilic attack of reagent on the phenolic group to give intermediate 252. Intramolecular C—C bond formation leads... 

The phenolic oxidation in the intra-molecular mode has been widely exploited as a synthetic tool for the construction of a spirodienone fragment. Kita and coworkers applied the oxidative coupling of various phenolic derivatives towards the synthesis of several pharmacologically interesting natural products [21,23,24]. In a recent example, spirodienone compounds 19, which are intermediates for the synthesis of an amaryllidaceae alkaloid, (+)-maritidine, were selectively obtained by the reaction of 18 and [bis(trifluoroacetoxy)iodo]ben-zene (Scheme 8) [24]. 

A similar oxidation of the phenol derivatives 20 bearing aminoquinones at the ortho positions affords the respective azacarbocyclic spirodienones 21 (Scheme 9) [23]. 

In a related study, the diphenolic substrate 409 was oxidized with a large excess of the iron complex [Fe(DMF)3Cl2][FeCl4] to give the spirodienone 413 in 35% yield (193). The oxidative phenolic coupling of 409 to furnish 413 using vanadium oxytrichloride had been previously reported, but the yield was slightly lower (176). Alkaline hydrolysis of 413 to cleave the A -trifluoroacetamide pro-... 

Asymmetric phenolic oxidative coupling.1 Oxidation of the chiral oxazolidine 1 with VOF3 results in efficient para-para coupling to a spirodienone 2. The trans-... 

Further oxidation of 43 leads to bis- or tris-spirodienone derivatives of calixarenes. They possess with the directionality of each spirodienone moiety an additional, independent stereogenic element. Thus, for a calix[4]arene derived bis(spirodienone) 45 six isomeric forms are possible, two meso forms and two pairs of C2-symmetric enantiomers, see Figure 8. The number of possible isomers increases with increasing of the number of rings in the macrocycle.92... 

Continuing interest in the development of preparatively useful anodic C-C bond-forming reactions has led to detailed investigations of the intramolecular trapping of phenoxonium ions by alkenyl side chains in anodic oxidation of phenolic biphenyl derivatives [56-58]. In this process, solvent trapping by methanol occurs after the phenoxonium ion has been intercepted by the side-chain 7r-bond. As shown in Table 3, a variety of substituted spirodienones (LVII) may be prepared from the corresponding phenolic biphenyls (LVI) under constant-current electrolysis conditions. 

The arylethylbenzylamine derivative (164) with one blocked para position was smoothly oxidized with alkaline ferricyanide to the spirodienone (165), related to the Amaryllidaceae alkaloid system. 

Intramolecular Cp—Car couplings have been observed in the anodic oxidation of a series of 4-hy-droxy-2-vinylbiphenyls, e.g. 293), which afforded the corresponding spirodienones (c.g. 294 92% from 293). Another Cp—Car linkage resulted from the brief oxidation of the dihydrocinnamyl cinna-mate (295) with thallium tristrifluoroacetate-catalytic boron trifluoride (water-quench), when the eight-membered lactone (296) was formed. ... 

The quinoline 325 was obtained in a dienone-phenol rearrangement of azaspirodienone 324 under vigorous conditions in the presence of an oxidizing agent (equation 155). The treatment of the spirodienone 326 with BF3 EtiO gives the 1,3-diazepine derivative 327 (73%) via a dienone-phenol rearrangement (equation 156). 

Arctigenin (472), prepared from 3,4-dimethoxybenzaldehyde, was submitted to PhI(OCOCF3)2-promoted oxidation in trifluoroethanol (TFE) (room temp., 24 h) to afford spirodienone 473 and a mixture of two cyclooctadienes (474 and 475) in 13 and 14% yields, respectively. When the reaction was repeated in hexafluoroisopropanol for 3.5 h, a 1 1 mixture of stegaue 474 and isostegane 475 was obtained in 26% yield (Scheme 93). Acid-catalyzed rearrangement of 473 with HCIO4 in CHCI3 provided a quantitative... 

Biomimetic syntheses of dibenzoazonines 635 and 636 were carried out by VOF3-mediated oxidation of diphenolic benzylisoquinoline 637 and its methyl ether 638, respectively. The diphenolic compound 637 was submitted to VOF3-mediated oxidation at — 10°C to afford in 40% yield the para-para coupled spirodienone 639, which was further converted to dibenzoazonine 635 (Scheme 122) ". Similar coupling reactions have also been carried out . ... 

A particularly direct synthetic entry to subtarget IV would materialize if a phenolic amide or amine such as Ilia or Illb could be induced to undergo oxidative cyclization to spirodienone IV, which could then be reduced to valuable synthetic intermediates. (Scheme 12). 

The synthesis of Ciufolini, published in 2001 [6], is based on the strategy he had previously developed to assemble the spirobicyclic skeleton through an oxidative cyclization of phenolic oxazolines (see 3.2.1). The strategic plan for the synthesis of FR901483 (1) is outlined in Scheme 21 and starts with the same disconnection C(7)-C(8) as used by Snider and Sorensen, involving a retroaldol process which leads to aldehyde 6. This advanced intermediate could be prepared from the spirodienone 49 available from an adequate oxazoline such as 50, which comes from two tyrosine units. 

The formation of spirodienone products by nonphenolic ben-zylisoquinoline oxidative anodic coupling (415) (yield 90%) and by facile biomimetic syntheses of aporphine and promorphinane alkaloids can proceed along the pathway outlined in Scheme 6 via the morphinanedienone... 

Biogenetic-type syntheses of ( )-oxocrinine (21a) and ( )-oxomaritidine (21b) by an anodic oxidation procedure have been achieved. Thus oxidation of the trifluoroacetyl derivative (22a) in acetonitrile solution using platinum electrodes and fluoroboric acid electrolyte gave the spirodienone (23a) in 62% yield. Compound (23a) was readily converted into ( )-oxomaritidine (21b) by known procedures. This represents the highest observed yield of a phenol oxidative... 

Protection of t-amines. Recent examples of use of amine borane complexes include the intramolecular oxidative phenol coupling of 1 to 2, a reaction that fails with the free amine. Several spirodienone precursors to aporphine and... 

The anodic oxidation of substituted bromophenols yields spirodienones e.g. 18. These undergo a Lewis acid catalysed rearrangement to chromans, the regiochemistry of which is dependent on the substituents present in the spiro compound (Scheme 19) <01T5533>. 

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