Chelotropic

Hoffmann and Schiittler (75CB844) attempted to generate methanoylcarbene by high-temperature chelotropic extrusion from a bicycloheptadiene derivative, but the only identified product was a very low yield of benzene. 

Hoffmann and Schiittler showed by C labelling (75CB844) that (81) generated by chelotropic extrusion from a bicycloheptadiene derivative did not isomerize to oxirene. This is as expected from MO calculations (Section 5.05.6.2). 

Thiirane 1,1-dioxides extrude sulfur dioxide readily (70S393) at temperatures usually in the range 50-100 °C, although some, such as c/s-2,3-diphenylthiirane 1,1-dioxide or 2-p-nitrophenylthiirane 1,1-dioxide, lose sulfur dioxide at room temperature. The extrusion is usually stereospeciflc (Scheme 10) and a concerted, non-linear chelotropic expulsion of sulfur dioxide or a singlet diradical mechanism in which loss of sulfur dioxide occurs faster than bond rotation may be involved. The latter mechanism is likely for episulfones with substituents which can stabilize the intermediate diradical. The Ramberg-Backlund reaction (B-77MI50600) in which a-halosulfones are converted to alkenes in the presence of base, involves formation of an episulfone from which sulfur dioxide is removed either thermally or by base (Scheme 11). A similar conversion of a,a -dihalosulfones to alkenes is effected by triphenylphosphine. Thermolysis of a-thiolactone (5) results in loss of carbon monoxide rather than sulfur (Scheme 12). 

Finally, it should be of interest that the rearrangements of several cyclic benzylic sulfinates have also been described in the literature by Durst46 and Hogeveen47, and seem to proceed by a special two-step mechanism retro-Diels-Alder extrusion of S02, followed by its chelotropic addition to the unstable quinodimethane intermediate (e.g. equation 10). 

The chelotropic elimination of nitrous oxide from N-nitroso-aziridines is a reaction restricted to this class of compounds... 

Heterocyclic analogs of ortho-quinodimethane have become increasingly popular for Diels-Alder functionalization of C60. Several methods for generating these highly reactive species have been developed however, most attention has been paid to their generation via chelotropic elimination of S02 from het-... 

Scheme 4.2 Diels-Alder cycloaddition of tetrachlorothiophene dioxide (4) and /V-ethyI maleimide (5) yields a high energy intermediate (6) that decomposes spontaneously by elimination of sulfur dioxide. The initially formed product is subsequently oxidized in situ. Transition states for cycloaddition and chelotropic S02 elimination closely resemble the hexachloronorbornene derivative 3 used as a hapten to elicit antibody 1 E9.

Scheme 3. The highly-ordered transition state associated with the Diels-Alder reaction has made it a natural target for work in the field of catalytic antibodies [15]. Indeed, Hilvert [15a] has reported recently the first successfully antibody-catalyzed Diels-Alder reaction. Monoclonal antibodies elicited to the boxed hapten 14 provided both acceleration of and multiple turnover of the cycloaddition between tetrachlorothiopene dioxide and IV-ethyl maleimide. The initial adduct decomposes by the chelotropic-extrusion of sulfur dioxide affording the dihydrophthalimide derivative 13...

Extrusion (or elimination) of sulfur from thiiranes and thiirenes is a facile process. Virtually all thiiranes and thiirenes, as well as their V-oxides and V,V-dioxides, undergo thermal extrusion of the sulfur moiety with increasing facility according to the trend S << SO < S02. Sulfur monoxide produced in this way can be utilized in cycloaddition processes, for example, from 2 in refluxing toluene with 2,3-dimethyl-l,3-butadiene in a chelotropic addition <1997JOC8366>. 

The book is divided into three parts. Part I deals with typical complex organic reactions such as (i) reactions involving carbocations and carbanions, (i/) Pericyclic and electrocyclic reactions and (ii/) Sigmatropic and Chelotropic reactions. This part also includes material useful for characterization of products from structural point of view such as Geometrical isomerism, Stereochemistry and Conformation. Part II is concerned with spectroscopic methods of structure determination such as U.V.,... 

Suarez et al. studied the mechanism of decomposition of ethene episulfone 42 and 2-butene episulfones 43 to SO2 and the appropriate ethene by means of ab initio computation <1996JPC13462>. Decomposition of the episulfones was stereospecific involving an asynchronous, chelotropic transition state. For ethene episulfone, the barrier to reach the transition state was between 28.68 and 32.52 kcal mol and the exothermicity was between —29.03 and —33.23 kcalmoF, depending on the computation method. The fact that the r-2-butene episulfone lost SO2 more rapidly than the /ra r-isomer, according to the calculations, was attributed to the dominance of attractive over repulsive dispersion forces between fir-methyl groups. 

The last procedure is particularly noteworthy beirause of the mild reaction conditions, which are compatible with various functional groups. The chelotropic, thermal elimination of sulfur dioxide, (547) (542), one of the oldest routes to o-quinodimethanes. remains attractive owing to the... 

Ab initio calculations at the MP2(FC)/6-31G //RHF/6-31G level show that the chelotropic reactions of 1,3-dienes with SO2 cannot he two-step as recently reported. 

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