Spirodienone compounds

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]. 

Electrooxidation is also viable for phenol ether-phenol ether coupling and has been thoroughly investigated. For example a range of compounds (65) with R = H or Me, Z = CH2 or O, = 1 or 2, reacted at the anode to give fair yields of the corresponding biaryls (66), together with spirodienone products (see Section 2.9.3.2). 

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 . ... 

Bis(pyridinium) iodotetrafluoroborate, as iodinating agent 651 Bis-resorcarenes 1420 A,A -Bis(salicyUdene)phenylene diamine, tautomerism in 359 Bis-spirodienones 1410, 1411 Bleaching mills, chlorinated phenolic compounds from 932 B3LYP/cc-pVTZ calculations 372-374 B3LYP/6-31G calculations 378, 383, 385 Boc-protection 1406... 

The calix-spirodienones undergo a variety of reactions and are useful intermediates for effecting alterations at the lower rim. Treatment with NH2NH2 at room temperature yields the bridged compound 242while under the more... 

The interesting stereochemical possibilities for the large-ring spherand-type calixarenes 16, which include compounds with >3 and symmetry, are discussed in ref. 14e. The intriguing stereochemistry of the calixarene spirodienones... 

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... 

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>. 

The transition state for the degenerate [3,3]sigmatropic rearrangement of the spirodienones (267) is postulated to be of the form (268). This is substantiated by the increased activation energy observed for compounds whose substituents impose substantial twisting constraints on this classical boat-like transition state. 

For the preparation of multiply phosphorus bridged systems, we studied the pyrolytic behavior of calixarene dialkyl phosphate ester derivatives. These compounds are useful intermediates for the OH-depletion of the calixarenes [15, 16] and for the preparation of aminocalixarenes [17]. These esters can be prepared by treatment of the calixarenes with a dialkyl chlorophosphate in the presence of base [18]. In the case of 1, under mild conditions, the distal (i.e, 1,3-) bis(diethyl phosphate ester) derivative is obtained (2a) while under more drastic conditions (CH2Cl2/aq NaOH, phase transfer catalysis) the tetraphosphate 2b is formed [15a]. Calixarene mono diisopropyl phosphate ester and l,2-bis(diisopropyl phosphate ester) derivatives (2c and 2d) were prepared by mono- or dideprotonation by LDA of the monospirodienone derivative 3 followed by treatment with the corresponding dialkyl chlorophosphate [15e, 17b]. Aromatization of the spirodienone products was achieved by heating or by their treatment with HBr yielding the dialkylphos-phate esters derivatives 2c and 2d [15e, 17b]. 

In contrast, irradiation of a dienone 20, which bears a carboxy group at C2, in dioxane gave the azulene dienone 23 and enone 24 in 67% and 16% yields, respectively, while under similar conditions the 4-carboxydienone 25 yielded the spirodienone 28 in 60% yield (Scheme 4). The ability of the carboxy group to internally protonate the carbonyl group at C3 in the zwitterionic intermediates 21 and 26 is likely to be the major factor driving the rearrangement to azulene or spiro compounds rather than to... 

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