Phenylthiyl radical addition

Where it is possible to distinguish the products, thiol additions show stereospecificity. The products of addition of hydrogen sulfide, thio-phenol, and thiolacetic acid to 1-chlorocyclohexene are to be 75%, 94%, and 66% cis-l, 2-disubstituted cyclohexane, respectively.88 The addition of thiolacetic acid is less stereopecific than the other thiols. The stereospecificity apparently depends upon the ratio of addendum to 1-chlorocyclohexene, Phenylthiyl radical addition to 1-methylcyclo-... 

The stereospecific substitution produces a sterically less strained product when a more bulky p-nitrophenyl substituent occupies the equatorial position and the less bulky phenylthiyl substituent occupies the axial position. Steric limitations of the nucleophile attack caused by strains in the final product are thus removed. And therefore, ion-radical addition ofp-nitrobenzyl radical to the lithium salts of 5-nitro-l,3-dioxanes proceeds stereospecifically (Zorin et al. 1983 Scheme 6.3). 

Radical attack on the central bond in [1.1.1 [propellane 1 occurs 2-3 times faster than attack on styrene96 and yields bridgehead bicyclo[l.l.l]pent-l-yl radicals6. Laser flash photolysis techniques were used to measure the rate constants for the reactions of la with five different radicals (Table 12)96"99. The addition of the phenylthiyl radical to la is... 

A potential method for the preparation of novel amino acids via the highly selective addition of radicals to the glyoxylic oxime derivative of Oppolzer s camphor sultam (88) has been reported.181 Both Lewis acid and non-Lewis acid-mediated reaction conditions for the addition of alkyl radicals generated from alkyl iodides and Et3B/Bu3SnH were examined. A new chiral auxiliary based upon (R,R)-2,5-diphenylpyiTolidine has been used in the addition of phenylthiyl radicals to unsaturated methacrylamides. The selectivity was found to be better than that reported for the structurally related 2,5-dimethylpyrrolidine derivative.182... 

A highly diastereoselective radical cascade involving addition of a phenylthiyl radical to a terminal alkyne followed by a [1,5]-hydrogen transfer and a 5-exo-cyclization (g) has been reported (Scheme 112).165... 

The synthesis of natural products has been accomplished by this strategy examples are shown in Eqs. (18), (19). The key step used by Keck and Wager in the total synthesis of en/-lycoricidine [43a] relies on the addition of phenylthiyl radical to the... 

The observation that thiyl radicals are able to isomerize alkenes was first made by Walling et al. many years ago [55] and, now the addition-elimination sequence of the phenylthiyl radicals is an established methodology in fine chemical synthesis [56]. It has been utilized as key step in the synthesis of biologically active compounds, such as (-)-gloeosporone [57a], (-l-)-hitachimycin [57b] and other naturally occurring macrolides [5b], as well as for preparing non-natural isomers of phospholipids [58]. 

The emphasis here is on the properties of glutathione (or cysteine if data for cysteine, but not GSH are available). Dithiols which form cyclic or stabilized disulphide radical anions, such as dithiothreitol (//ireo-l,4-dimercapto-2,3-butanediol) [29-33], or the reduced form of lipoic acid (6,8-dithiooctanoic acid) [15, 34-37], in effect have uncharacteristically high values of to be good models for glutathione. In addition, biological effects may be complicated by thiol/disulphide exchange since these thiols will reduce many disulphides [38-40]. Arenethiyl radicals (e.g. phenylthiyl or derived from 2-mercaptoimidi-azole) are closer to phenoxyl radicals in nature than aliphatic thiyl radicals [41-44]. 

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