Allyl peroxides

Peroxyacetals 58 and peresters such as 61 are also effective transfer agents, however, at typical polymerization temperatures ( 60 C) they are thermally unstable and also act as initiators. Compounds such as 62 which may give addition and 1,5-intramolecular substitution with fragmentation have also been examined for their potential as chain transfer agents (1,5-Sh/ mechanism).  

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In the case of allyl peroxides (12 X= CH2, A=CH2, BO),1 1 1 intramolecular homolytic substitution on the 0-0 bond gives an epoxy end group as shown in Scheme 6.18 (1,3-Sn/ mechanism). The peroxides 52-59 are thermally stable under the conditions used to determine their chain transfer activity (Table 6.10). The transfer constants are more than two orders of magnitude higher than those for dialkyi peroxides such as di-f-butyl peroxide (Q=0.00023-0.0013) or di-isopropyl peroxide (C =0.0003) which are believed to give chain transfer by direct attack on the 0-0 bond.49 This is circumstantial evidence in favor of the addition-fragmentation mechanism. 

Depending on the choice of transfer agent, mono- or di-cnd-functional polymers may be produced. Addition-fragmentation transfer agents such as functional allyl sulfides (Scheme 7.16), benzyl ethers and macromonomers have application in this context (Section 6.2.3).212 216 The synthesis of PEG-block copolymers by making use of PEO functional allyl peroxides (and other transfer agents has been described by Businelli et al. Boutevin et al. have described the telomerization of unsaturated alcohols with mercaptoethanol or dithiols to produce telechelic diols in high yield. 

Usually the allylic peroxides are not the final products but they are reduced to allylic alcohols as in the synthesis of E-5-cyclodecenone (6.14)620). 

Towards the end of this section it may be worthwhile to point out some new reactions with high-valent metals and TBHP. The first is a pyridinium dichromate PDC-TBHP system134. Nonsubstituted or alkyl-substituted conjugated dienes, such as 1,3-cyclooctadiene (87) and others (also linear dienes), yield keto allyl peroxides 88 (equation 18), whereas phenyl-substituted dienes such as 1,4-diphenylbutadiene (89) gave diketo compounds, 90 (equation 19). In further research into a GIF-type system135 with iron and TBHP, limonene gave a mixture of products with carvone as the major product. The mechanism is thought to proceed initially by formation of a Fe(V)-carbon... 

Cyclic allyl peroxides are converted stereoselectively into the dihydroxypropyl peroxides using a modified Sharpless procedure with osmium tetroxide and /-butyl peroxide in the presence of benzyltrimethylammonium acetate [23]. Yields are generally good with exclusive an/f-addition with respect to the peroxy group, although both the steroselectivity and yield (<40%) are poor for the oxidation of 2,3-dihydrofuran-3-yl peroxide and 2,3-dihydro-4//-pyran-4-yl peroxide. 

BOBZIB) Alkyl allyl peroxides, alkyl benzyl peroxides, and allyl propargyl peroxides l-Metbyl-6,10-dimetbylene-9-metbylperoxy-4-oxatricyclo[7.4.0.0 ]tridecan-5-one 1.478 151.7 150... 

The present volume comprises 17 chapters, written by 27 authors from 11 countries, and deals with theoretical aspects and structural chemistry of peroxy compounds, with their thermochemistry, O NMR spectra and analysis, extensively with synthesis of cyclic peroxides and with the uses of peroxides in synthesis, and with peroxides in biological systems. Heterocyclic peroxides, containing silicon, germanium, sulfur and phosphorus, as well as transition metal peroxides are treated in several chapters. Special chapters deal with allylic peroxides, advances in the chemistry of dioxiranes and dioxetanes, and chemiluminescence of peroxide and with polar effects of their decomposition. A chapter on anti-malarial and anti-tumor peroxides, a hot topic in recent research of peroxides, closes the book. 

The HPLC method with CLD described in Section V.B.2.C for determination of hydroperoxides using luminol (124) with hemin (75a) catalysis is ineffective with dialkyl peroxides, such as di-r-butyl peroxide, cumyl propyl peroxide and cumyl 3-phenylpropyl peroxide. However, for a certain set of experimental conditions, cumyl allyl peroxide can be determined, but the sensitivity is much lower than for hydroperoxides164. 

According to the authors, the importance of the various reactions in this scheme depends on the catalyst properties, particularly the possibility of reaction between the allyl radical (complex) and lattice oxygen and the possibility of desorption of an allyl peroxide species. 

Oxidation of allylic alcohols with singlet oxygen has been used as a route to prepare allylic peroxides in a stereoselective fashion (equation 46)189. 

The rearrangement of tertiary peroxides to secondary allylic peroxides is irreversible and exothermic, whereas the reactions of secondary to secondary or secondary to primary peroxides give mixtures of allylic peroxides. 

A second characteristic reaction of singlet oxygen is the ene reaction with olefins with an allylic hydrogen to give allylic peroxides. Thus 2,3-dimethyl-hutene-2 (3) is converted in 53% yield into the allylic peroxide 2,3-dimethyl-3-liydroperoxybutcnc-l (4) ... 

Table 6.10 Transfer Constants for Allyl Peroxide and Related Transfer Agents at...

An asymmetric total synthesis of the marine product plakorin (52), a 1,2-dioxin, is based upon a hydroxy-directed addition of IO2 and radical rearrangement of the resulting allylic peroxide <97JA3824>. 

There is little or no thermochemical property data available for unsaturated alkylperoxy and peroxide species. Peroxides are often impure and/or instable, and therefore difficult to isolate and characterize by experimental methods. There is no experimental data on vinyl, phenyl, ethynyl, or allyl peroxides that we are aware of. Experimental studies on the reaction of vinyl radical and allyl radical with O2 to form the corresponding peroxy radical have been reported by Gutman et al. [11, 12]. The phenyl-peroxy radical was reported by Lin s group as a major product in the phenyl radical reaction with O2 at ambient temperatures [17]. 

The Cd—C rotation barrier in allyl hydroperoxide (CH2=CH—CH2OOH) is higher (6.4 kcal mol ) which is 3 times the corresponding rotational barrier for allyl peroxide (CH2=CH— CH2OOCH3). Both have one-fold symmetry. 

Allylic peroxides can also undergo 1,3-peroxyl transfer either by a concerted (one step) pathway (8) ... 

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