Radicals methoxymethyl

In model studies directed towards the synthesis of ( )-gelsemine, 5-exo-trig cyclization of an aryl radical, derived from the vinylogous uretane 58, onto a methoxymethyl enolether resulted in partial fragmentation of the intermediate... 

Conversion of 3-Deoxyglucose-derived Radicals into Prostanoid Cyclopentanes [14] [(2R)-(2a.,4a, 5, 6a,7afi)]-Hexahydro-5-(methoxymethyl)-2-phenyl-6-(phenylmethoxy)cyclopenta-l,3-dioxin (6b, Y = OMe)... 

When other free radical processes are available, the mixture of products becomes more complicated. For instance, 0-(methoxymethyl)phenylsilacyclobutane, when irradiated, is proposed to undergo a competing loss of ethylene to yield silene and migration of the methoxy group from the benzylic carbon to silicon, leading to the mixture of products (Scheme 6) <2003JA8096>. 

N,N-Dimethylaniline (DMA) forms N-methoxymethyl-N-methylaniline (34) and N,N-bis (methoxymethyl)-aniline (35) in methanol-NaOCH3 as SSE in an ECgECN sequence, while in neutral medium with NH4N03/MeOH as SSE N,N,N ,N -tetramethylbenzidine (36) is formed via an EC-mechanism by dimerization of the intermediate radical cation 37 (Eq. (104) ) 248) ... 

Attention was centered on radical precursors in which the 3-pyridyl moiety was attached at the indole-3-position with the aim of directly producing the pyrido[4,3-b]carbazole skeleton of ellipticine by regioselective cyclization upon the 4-position of the pyridine ring. Satisfactorily, A-methyl and A-benzyl selenoesters 52a and 52b led to the ellipticine quinones 53a and 53b in acceptable yields (60 and 42% yield, respectively), after the radical cyclization and the in situ oxidation at the interannular methylene group. The cyclization was clearly less efficient from A-(methoxymethyl) selenoester 52c and no reaction was observed... 

The reductive cyclization protocol was then applied to a suitably A-protected radical precursor to allow further access to the alkaloid calothrixin B. Satisfactorily, 2-indolylacyl radicals derived from A-(methoxymethyl) selenoester 57 underwent cyclization under TTMSS-AIBN conditions with an even higher efficiency than their A-methyl counterparts. The reaction nevertheless followed a different course as, after the radical addition and quinoline rearomatization, pentacyclic phenol 58, a fully aromatic tautomeric form of ketone P, was isolated in 90% yield. The same phenol 58 was isolated although in lower yields (50-70%) using either stannane-AIBN or AIBN-irradiation protocols. 

A similar well-defined graft copolymer consisting of polystyrene main chain and branches (G-7) can be prepared simply via repetition of copper-catalyzed living radical polymerizations.209 Thus, the synthesis starts with the copolymerization of styrene and />(acetoxymethy 1)styrene or />(methoxymethyl)sty-rene, followed by bromination of the substituent into the benzyl bromide moiety, which then initiates the copper-catalyzed radical polymerization of styrene to give graft polymers with 8—14 branches. 

A mechanistic study of in.itial C-C bond formation in the methanol conversion reaction is reported. Reaction of methanol with added hydrogen using W0,/A1203 and H-ZSM-5 catalysts does not significantly alter the product distribution from that of normal methanol conversion. This is considered to be clear evidence against the involvement of a gas phase methylene intermediate. In addition the behaviour of the methoxymethyl radical in the gas phase has been studied and the results demonstrate that this species is also not involved as an intermediate in initial C-C bond formation. 

Dimethyl ether was reacted over a radical initiator, pre-dried dibenzoyl peroxide supported a celite, at various temperatures (Table 2). Although dibenzoyl peroxide was short lived under these conditions sufficient was reactive in the timescale of the experiments, typically 5 min. Under all conditions only dimethoxyethane was observed as a dimerisation product showing that the methoxymethyl radical was generated under these conditions. The absence of other products, e.g. alkenes or ethanol, discounts the methoxymethyl radical fragmentation/recombination pathway (mechanism 1, Fig. 1). 

These results show that dimethoxyethane, generated from the dimerisation of methoxymethyl radicals, is not a suitable ethene precusor and hence mechanism 2 (Fig. 1) can also be discounted as a plausible possibility. 

The results of this study using addition of hydrogen or model studies of the methoxymethal radical give clear evidence against the involvement of a gas phase carbene or methoxymethyl radical intermediates in the mechanisms of initial C-C bond formation in the methanol to gasoline conversion reaction. 

Comparable results are obtained in radical additions to several C2-symmetric fumaric bisamidcs. 2,5-Dimcthylpyrrolidine14,15,2°, 2,5-bis(methoxymethyl)pyrrolidine and 1,3 4,6-di-0-benzylidene-2,5-dideoxy-2,5-imino-L-idit21 are used as chiral auxiliaries. Reactions with cyclohexyl or tort-butyl radicals, generated by the mercury or the tin method, respectively, proceed with high levels of asymmetric induction, yielding essentially only one of the two possible products. 

Oxidation potentials for radicals have been determined by photomodulation voltammetry to be in the range of -1.03 V (vs see) for the A, A -dimethylamino-methylradical, —0.24 V for methoxymethyl, 0.09 V for fbutyl, 0.35 V for diphe-nylmethyl, 0.73 V for benzyl, <0.99 V for ethyl and <2.49 V for methyl [137]. In anodic addition of anions to double bonds it has been found that, depending on the oxidation potential of the adduct radical, either radical- or carbocation-derived products are obtained (Section 2.6.3.4). 

Radicals can be generated by cathodic reduction from carbocations, protonated C=X bonds, and the reduction of halides or onium salts. The reduction potentials of carbocations range from 1.87 V (vs nhe) for NCCH(4-CN-C6H4)+, 0.97 V for the benzylcation, 0.33 V for the tert-butyl cation, and 0.0 V for the methoxymethyl-cation to -0.88 V for Et2N=CHCH3+ [143],... 

A prochiral radical intermediate is generated from a-methoxymethyl-a-iododihy-drocoumarin (la) which is coordinated via the carbonyl oxygen to the chiral Lewis acid/ligand combination of MgL and 2. Enantiomeric excesses of up to 62% and yields of 88% have been obtained in this enantioselective reduction using tributyltin... 

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