Sulfur dioxide, extrusion dioxides

Interestingly, benzonitrile oxide does not react with thiirene dioxide 19b even in boiling benzene, whereas the electron-rich diene l-piperidino-2-methyl-l, 3-pentadiene (177) does react under the same reaction conditions to give the expected six-membered [4 + 2] cycloadduct 178, accompanied by sulfur dioxide extrusion and 1,3-hydrogen shift to form the conjugated system 179175 (equation 70). 

Three types of photoextrusion reactions have been identified in the irradiation of aryl-substituted 1,3,2-dioxathiolane 2-oxides [5 1-1-2 4-2] cycloelimination to produce a carbonyl compound, a carbene and sulfur dioxide extrusion of sulfur dioxide accompanied by a pinacol-like rearrangement to yield an aldehyde or ketone and extrusion of sulfur trioxide to give an alkene <72JOC2589>. Sensitization and quenching experiments indicate that a singlet state is responsible for the cycloelimination reaction, whereas the rearrangement and sulfur trioxide extrusion reactions arise from a triplet state <82JCR(S)175>. 

Examples of cycloadditions with more than six electrons are relatively rare detailed mechanistic information is in most cases not available. The stereochemistry of the 6 + 2 cheleotropic sulfur dioxide extrusion shown in Equations... 

Various cyclooctatetraenes have been also prepared by this sequential [67t+2rt] cycloaddition and sulfur dioxide extrusion, as shown in Scheme 6. 

Patonay, T. Hegediis, L. Patonay-Peli, E. Flavonoids. 43. Deprotonation-initiated aryl migration with sulfur dioxide extrusion a... 

It should be noted that if a 4,4-disubstituted /3-sultam is submitted to a desilylation reaction, decomposition is observed (Equation 7). This can be explained by fluoride-catalyzed desilylation followed by fluoride-catalyzed sulfur dioxide extrusion and elimination of hydrazine-1,2-dicarboxylate <2004HCA1574>. 

This strategy has also been extended to [6 + 2]-cycloaddition [61]. Thus, substituted cyclooctatetraenes can be prepared in two steps employing a Cr-(0)-promoted [67t + 27t] thiepin dioxide-alkyne cycloaddition, followed by photoactivated sulfur dioxide extrusion (Scheme 9.37) [62]. 

Pyridinophane 2 has also been synthesized in a four-step procedure which includes a pyrolytic sulfur dioxide extrusion as illustrated in Scheme 15). The UV photoelectron spectrum of 2 has been studied on the basis of a pertubational molecular orbital analysis and indicates the presence of through-space and through-bond interactions between the two pyridine rings. This finding has also been substantiated by CNDO/2 calculations. In addition, there appears to be a strong interaction between the nitrogen lone pairs and the n-system of the rings 6). 

Sulfur dioxide extrusion has been reported only for CpFe(CO)aS-(0)aCeF5 [Eq. (32)], This desulfination can be effected either photo-chemically or thermally in toluene at reflux (43). Other CpFe(CO)aS-(O)aR complexes [R = CCI3 43), Me, CHaPh, and Ph (JJ)] resist loss... 

Sulfur dioxide extrusion from -MeCaH4S(0)2Pt(PPh3)2Cl (31) and fraMr-Pt(PMe2Ph)2[S(0)2C6H4Me- ]Cl 20) has been effected, respectively, by heating at 200°-210°C and at reflux in toluene solution. 

Reactions initiated by electrophilic or oxidative attack at the ring sulfur atom (Scheme 4) are considered in the present review only if intermediates 19, such as 5-oxides or 5-dioxides, are not isolated but are transformed to the sulfur-free ring contraction product without prior isolation. Thus, sulfur dioxide extrusion from such isolated 5,5-dioxides as thietane 5,5-dioxide 21 or the Ramberg-BScklund reaction of a-halosulfonyl compounds (e.g., of 23) (770R1) (Scheme 5) are not included (for reviews on SO2 extrusions from heterocycles, see 90MI1 92MI1). 

Sulfur dioxide extrusion (desulfonation) from sulfolenes provides a useful procedure for generation of the diene in the presence of a dienophile, thus facilitating in situ Diels-Alder cycloadditions as illustrated by Scheme 72. The reaction in Scheme 72 involves the in situ formation of 2-cyanobutadiene (181) which then undergoes [4+2] cycloaddition with the dienophile maleimide to yield the adduct (182). 

In one case a cyclopropyl sulfone was converted to the corresponding cyclopropane by photochemical sulfur dioxide extrusion. Examples of Raney nickel desulfurization can be found in refs 921 and 922,... 

Thiophene 1,1-dioxidcs bearing electron-withdrawing substituents undergo a cycloaddition reaction with benzocyclopropene in tetrahydrofuran followed by sulfur dioxide extrusion to give annulenes 3 in 5-35% yield. The unsubstituted thiophene 1,1-dioxide is, however, not sufficiently reactive and undergoes dimerization rather than cycloaddition. ... 

BTF and its mono- and dichloro derivatives are very useful for conducting thermal reactions (Scheme 6), as illustrated by the sulfur dioxide extrusion reaction... 

The sulfone is a versatile functional group comparable to the carbonyl functionality in its ability to activate molecules for further bond construction, the main difference between these two groups being that the sulfone is usually removed once the synthetic objective is achieved. The removal most commonly involves a reductive desulfonylation process with either replacement of the sulfone by hydrogen (Eq. 1), or a process that results in the formation of a carbon-carbon multiple bond when a P-functionalized sulfone, for example a (3-hydroxy or (3-alkoxy sulfone, is employed (Eq. 2). These types of reactions are the Julia-Lythgoe or Julia-Paris-Kocienski olefination processes. Alkylative desulfonylation (substitution of the sulfone by an alkyl group, Eq. 3), oxidative desulfonylation (Eq. 4), and substitution of the sulfone by a nucleophile (nucleophilic displacement, Eq. 5) are also known. Finally, p-eliminations (Eq. 6) or sulfur dioxide extrusion processes (Eqs. 7, 8 and 9) have become very popular for the... 

Ruthenium-catalyzed asymmetric addition of alkane- or arenesulfonyl chlorides to styrenes leads to optically active suifones22,23. When this conversion is conducted under mild conditions no C —C bond is formed, however, at higher temperatures (100 =C), enantioselective asymmetric carbohalogenation of styrene with trichloromethanesulfonyl chloride (accompanied by sulfur dioxide extrusion) can be achieved with tetrachlorotris[( + )- or (—)-Diop]diruthenium. Excellent yields (up to 100%), but only low asymmetric inductions (up to 13 %), arc observed12. Similar results are obtained with carbon tetrachloride. A mechanism with radical formation w ithin the metal coordination sphere ( radicaloid ) has been proposed. 

The role of one of the vinyl groups can be played by a double bond of furan ring <89T302l>, the rearrangement results in the formation of a dihydrofuro[3,2-c]oxepin. Sulfur dioxide extrusion from tricyclic epoxide obtained from 3-thiabicyclo[3.2.0]hept-6-ene 3,3-dioxide (Scheme 22) affords 4,5-dihydrooxepin in 55% yield <82CC1164>. 

Sulfur dioxide extrusion from monosubstituted sulfolenes 261... 

Sulfur dioxide extrusion from 2,5-disubstituted sulfolenes 263... 

Sulfur dioxide extrusion from 3,4-disubstituted sulfolenes 266... 

Sulfur Dioxide Extrusion from Monosubstituted Sulfolenes... 

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