Abnormal Four-Membered Ring Formation in Intramolecular Radicalic Cyclization. High Stability of the Alkyl Radical Substituted with Methylthio and p-Tolylsulfonyl Groups

Abstract

Treatment of 5-iodo-1-(methylthio)-1-(p-tolylsulfonyl)-1-pentene with (n-Bu)3SnH and AIBN gave [(methylthio)(p-tolylsulfonyl)methyl]cyclobutane. This is due to the stability of an intermediary radical attached to methylthio and p-tolylsulfonyl groups.

Tributyltin Hydride-Mediated Free-Radical Cyclization of Allene-Tethered Oxime Ethers and Hydrazones

“…The formation of products 25d,e may be explained by the attack of the tin radical on the less substituted trigonal carbon of the allenic function. The very reactive vinyl radical B adds to the carbon atom of the hydrazone in an unusual 4- exo - trig addition. , This cyclization is facilitated by the presence of the gem -dimethyl group on the α-carbon atom of the hydrazone function, in agreement with recent similar reports . The cyclobutyl aminyl radical C fragments immediately into products 25d,e with subsequent elimination of the tributyltin group …”

Density Functional Theory Calculations of the Effect of Fluorine Substitution on the Cyclobutylcarbinyl to 4-Pentenyl Radical Rearrangement

“…In contrast to the extensive literature related to the above-mentioned radical systems, cyclobutylcarbinyl (CBC) radical ring openings and the respective reverse process, 4-exo cyclizations of 4-pentenyl radicals, have received much less attention. Kinetic studies of this exothermic ring-opening process have been confined to the parent system and a few methyl- and phenyl-substituted derivatives, − whereas 4-pentenyl cyclizations are generally observed only when a stabilized radical is formed in the process, − such as the example below where one of the few available rate constants for such a process was obtained: ,

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Photochemical Alkylation of Ketene Dithioacetal S,S-Dioxides. An Example of Captodative Olefin Functionalization

“…However, our attempt to alkylate these molecules through classical tin hydride methods, both thermal or photochemical, led to no result (in contrast vinyl sulfones undergo easy radical chain alkylation under these conditions) 15e. We feel that this can be rationalized by the peculiar captodative stabilization of the adduct radical . It has previously been shown that captodative radicals are poor hydrogen abstractors and easily dimerize.…”

“…These, in turn, are convenient synthetic intermediates in view of several possible elaborations, e.g., C -alkylation and -arylation, substitution of an allyl for a sulfone group, desulfurization, , pyrolysis to yield a carbonyl derivative, Pummerer rearrangement . Ketene dithioacetal S , S -dioxides have been shown to act as efficient acceptors of carbenes as well as of 1-hydroxy- (or alkoxy-)alkyl radicals. , Furthermore, intramolecular radical addition of β-(ω-iodoalkyl) derivatives has been shown to occur under classic radical chain conditions yielding five-, six-, and also four-membered cyclic derivatives, a result rationalized on the basis of the peculiar stability of the adduct radical due to the captodative effect . Somewhat surprisingly, no corresponding intermolecular radical alkylation has been reported except for the above-mentioned case of hydroxyalkyl radicals.…”