Olefinic peroxides, reduction

Recently, a novel porphyrin-based polymer, namely a poly(CO-Ru(n)-64) (with CO-Ru(n)-64 = ruthenium carbonyl spirobifluorenylporphyrin), was prepared electrochemically and used for the transfer of carbene to olefins and sulphides in a solid-state reaction. In another original study, a bimetallic porphyrin film using 65 was studied as electrode modifier with catalytic activity for molecular oxygen reduction and hydrogen peroxide reduction " . 

Epoxides can be readily made from enones with alkaline hydrogen peroxide, and so enone double bonds can be protected in preference to isolated double bonds. Wettstein [52, 53] used an enone epoxide in his aldosterone synthesis for protection during oxidative cleavage of another olefinic bond. He regenerated the olefin by reduction-dehydration. Crabbe... 

The stereochemical course of reduction of imonium salts by Grignard reagents was found to depend on the structure of the reagent 714). Hydro-boration of enamines and oxidation with hydrogen peroxide led to amino-alcohols (7/5). While aluminum hydrogen dichloride reacted with enamines to yield mostly saturated amines and some olefins on hydrolysis, aluminum hydride gave predominantly the unsaturated products 716). 

Although the biosynthetic cascade hypothesis predicts the co-occurrence of endiandric acids D (4) and A (1) in nature, the former compound was not isolated until after its total synthesis was completed in the laboratory (see Scheme 6). Our journey to endiandric acid D (4) commences with the desilylation of key intermediate 22 to give alcohol 31 in 95% yield. The endo side chain is then converted to a methyl ester by hydrolysis of the nitrile to the corresponding acid with basic hydrogen peroxide, followed by esterification with diazomethane to afford intermediate 32 in 92% overall yield. The exo side chain is then constructed by sequential bromination, cyanide displacement, ester hydrolysis (33), reduction, and olefination (4) in a straight-... 

Epoxidation of substituted spiro[cyclopentane-l,9 -fluorene]-2-enes 68 with a peroxidic reagent was studied [98], The spiro olefins react with m-chloroperbenzoic acid (mCPBA) in chloroform at 3 °C to give a mixture of the epoxides. In all cases (2-nitro (68b), 4-nitro (68c), 2-fluoro (68d) and 2-methoxyl (68e) groups), the iyn-epoxides, i.e., the syn addition of the peroxidic reagent with respect to the substituent, is favored. For example, for 6 nsyn anti = 63 31 for 68c syn anti = 65 35. Thus, a similar bias is observed in both the reduction of the carbonyl derivatives of 30 and the epoxidation of the derivatives of 68. 

The reductive elimination of a variety of )3-substituted sulfones for the preparation of di-and tri-substituted olefins (e.g. 75 to 76) and the use of allyl sulfones as synthetic equivalents of the allyl dianion CH=CH—CHj , has prompted considerable interest in the [1,3]rearrangements of allylic sulfones ". Kocienski has thus reported that while epoxidation of allylic sulfone 74 with MCPBA in CH2CI2 at room temperature afforded the expected product 75, epoxidation in the presence of two equivalents of NaHCOj afforded the isomeric j ,y-epoxysulfone 77. Similar results were obtained with other a-mono- or di-substituted sulfones. On the other hand, the reaction of y-substituted allylic sulfones results in the isomerization of the double bond, only. The following addition-elimination free radical chain mechanism has been suggested (equations 45, 46). In a closely related and simultaneously published investigation, Whitham and coworkers reported the 1,3-rearrangement of a number of acyclic and cyclic allylic p-tolyl sulfones on treatment with either benzoyl peroxide in CCI4 under reflux or with... 

The reduction of thiocarbonyl derivatives by EtsSiH can be described as a chain process under forced conditions (Reaction 4.50) [89,90]. Indeed, in Reaction (4.51) for example, the reduction of phenyl thiocarbonate in EtsSiD as the solvent needed 1 equiv of dibenzoyl peroxide as initiator at 110 °C, and afforded the desired product in 91 % yield, where the deuterium incorporation was only 48% [90]. Nevertheless, there are some interesting applications for these less reactive silanes in radical chain reactions. For example, this method was used as an efficient deoxygenation step (Reaction 4.52) in the synthesis of 4,4-difluoroglutamine [91]. 1,2-Diols can also be transformed into olefins using the Barton-McCombie methodology. Reaction (4.53) shows the olefination procedure of a bis-xanthate using EtsSiH [89]. 

Allylic acetates are usually prepared by esterification from allylic alcohols. However, the corresponding alcohols are often only accessible by the fairly expensive hydride reduction of carbonyl compounds. Consequently, direct allylic functionalization of easily available olefins has been intensively investigated. Most of these reactions involve peroxides or a variety of metal salts.However, serious drawbacks of these reactions, (e.g. toxicity of some metals, stoichiometric reaction conditions, or nongenerality) may be responsible for their infrequent use for the construction of allylic alcohols or acetates. 

A study of the photoaddition of formamide to olefins was undertaken with the aim of finding a new process for converting olefins to higher amides and possibly further to amines by reduction or by the use of the Hofmann rearrangement. Since hydrolysis of the amides to the corresponding carboxylic acids can be effected by standard procedures, this reaction provides a new process for carboxylation of olefins under mild conditions at room temperature. A similar reaction has been shown to take place in a thermal process, using peroxides as initiators (60). 

Similarly the dixanthate olefin synthesis, which works well with tin hydride, can also be performed with Ph2SiH2.19 Reduction of dixanthate 24 (B = adenosine) in refluxing toluene afforded 25 (B = adenosine) in 95 % yield. Initiation was by AIBN or benzoyl peroxide. 

DMF)Ru(0EP)02 (8, 135) can be formed from molecular 02, while Ti(0EP)02 (136) and Mo(TPP)(02)2 (137) can be made from peroxide addition [TPP = tetraphenylporphyrin, OEP = octaethylporphyrin]. The Ru system is ineffective for oxidation of terminal olefins at least under the mild conditions (1 atm 02, 35°C) studied thus far even the ubiquitous substrate triphenylphosphine is not oxidized catalytically because of formation of a relatively inert Ru(OEP)(PPh3)2 complex (138). The catalytic potential for 02 activation by Ru(II) porphyrins compared with Fe(II) porphyrins seems considerable, at least in principle, in view of a more readily accessible oxidation state of IV (139) this could circumvent the unfavorable one-electron reduction of 02 to superoxide (140). Such systems seem promising generally in terms of the multi-electron redox processes that 02 displays (141). 

The asymmetric total synthesis of the natural enantiomer (—)-nakadomarin A was completed by Nishida et al. in 2004 (Scheme 8.12) [82]. Diels-Alder reaction between siloxydiene 173 and chiral dienophile 172 (prepared from L-serine in 10 steps [83]) gave the highly functionalized key intermediate hydroisoquinoline 174, which was subjected to Luche reduction, cyclization, and HCl treatment to furnish the tricyclic intermediate 175. Compound 175 was converted to 177 via ozonolysis cleavage of ring B followed by recyclization of the unstable bisaldehyde to a five-membered ring by aldol condensation. The Z-olefin 178 was obtained from Wittig reaction of 177, and was further converted to furan 180 via peroxide 179. The... 

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