Allylic vinylic sulfones

King and Harding296 have reported an interesting Sulfo-Cope rearrangement, and have presented evidence for the formation of the unstable sulfene (142) during the gas or liquid phase thermal [3,3]sigmatropic rearrangement of allyl vinyl sulfone (equation 88). 

Thermal [3,3] rearrangement of allyl vinyl sulfones, the sulfo-Cope rearrangement (equation 27), proceeds readily in the liquid phase above 165 °C, and has the potentially useful synthetic feature of generating a new carbon-carbon bond120. 

The electron richness of the sulfur atom can be further decreased by introduction of a higher oxidation state. The thermolysis of allyl vinyl sulfone, at rather high temperature, was shown to give the corresponding sulfene, which was trapped by appropriate reagents [113]. 

Similarly, enamino vinyl sulfones (345) can undergo a thermally allowed electrocyclic reaction between the termini of the enaminic double bond and the allyl sulfonyl portion in the intermediate anion (346) to afford a, /1-unsaturated thiene dioxides (348) as shown in equation 126335. 

Ueno and coworkers10 have found that the facile displacement of sulfonyl group from a-alkylated allyl p-tolyl sulfones 18 by tri-n-butyltin radical in the presence of 2,2 -azobis[2-methylpropanenitrile] (AIBN) occurs smoothly in refluxing benzene (equation 11). In contrast, vinyl sulfones undergo the radical substitution reaction to give vinylstannanes in the presence of AIBN at a higher temperature11. 

An example for synthesis of the chiral [l-keto ester 69 is illustrated in equation 64. It involves conjugate addition of the dipotassium / -keto ester 68 to vinyl sulfone 67 followed by in situ quenching with allyl bromide54. The method provides a new procedure to sevenring annulation product 70 that is a potential precursor for (l)-(-)-cytochalasin C. 

Vinyl sulfones such as 262 are smoothly converted to a,) -unsaturated nitriles such as 263 on treatment with KCN in the presence of dicyclohexyl-18-crown-6 in refluxing t-butyl alcohol (equation 155)148. The reaction conditions are compatible with base-labile functionalities such as a methoxycarbonyl group (equation 156)148. This method can be used in the preparation of the sesquiterpene aldehyde nuciferal from allyl phenyl sulfones. 

The aziridine aldehyde 56 undergoes a facile Baylis-Hillman reaction with methyl or ethyl acrylate, acrylonitrile, methyl vinyl ketone, and vinyl sulfone [60]. The adducts 57 were obtained as mixtures of syn- and anfz-diastereomers. The synthetic utility of the Baylis-Hillman adducts was also investigated. With acetic anhydride in pyridine an SN2 -type substitution of the initially formed allylic acetate by an acetoxy group takes place to give product 58. Nucleophilic reactions of this product with, e. g., morpholine, thiol/Et3N, or sodium azide in DMSO resulted in an apparent displacement of the acetoxy group. Tentatively, this result may be explained by invoking the initial formation of an ionic intermediate 59, which is then followed by the reaction with the nucleophile as shown in Scheme 43. 

Vinylic sulfones undergo the same reaction especially when allylic, benzylic or t-alkylithium reagents are employed. One case of a vinyl sulfone deserves special mention - . When phenyl trans-3-bromopropenyl sulfone is treated with certain Grignard reagents it undergoes an alkylating cyclization ... 

Vinyl ethers can also be generated by thermal elimination reactions. For example, base-catalyzed conjugate addition of allyl alcohols to phenyl vinyl sulfone generates 2-(phenylsulfinyl)ethyl ethers that can undergo elimination at 200° C.223 The sigmatropic... 

These two products must be formed via an S -type substitution of intermediate 201, which may be formed by the nucleophilic attack of benzenesulfmate with 1,2-pro-padienyl phenyl sulfone. This was further supported by the reaction of 1-methyl-1,2-propadienyl sulfone with bis(phenylsulfonyl)methane in the presence of sodium benzenesulfmate, in which allylic sulfone 202 and vinylic sulfone 203 were formed [103],... 

Phenylsulfonylpropadiene can even react with certain tertiary amines such as 213 via cleavage of the allylic C-N bond in the amine followed by conjugate addition and coupling to afford vinylic sulfones 215 [114]. 

A more recent synthesis of 197 [365] is shown in Fig. 9. Enders introduced the stereogenic centre of (S)-lactic acid into the crucial position 10 in 197. The vinylsulfone B, readily available from lactic acid, was transformed into the planar chiral phenylsulfonyl-substituted (q3-allyl)tetracarbonyliron(+l) tetra-fluoroborate C showing (IR,2S,3 )-configuration. Addition of allyltrimethyl silane yielded the vinyl sulfone D which was hydrogenated to E. Alkylation with the dioxolane-derivative of l-bromoheptan-6-one (readily available from 6-bro-mohexanoic acid) afforded F. Finally, reductive removal of the sulfonyl group and deprotection of the carbonyl group furnished 197. A similar approach was used for the synthesis of 198 [366]. 

Type III (no homodimerization) Acrylonitrile," protected 3° allylamines" Vinyl trialkoxysilanes, vinyl siloxanes 1,1-Disubstituted olefins, " non-bulky trisubstituted olefms, vinyl phosphonates, " vinyl phosphine oxides,phenyl vinyl sulfone, acrylonitrile, 4° allylic carbons (all alkyl substituents), protected 3° allylic alcohols, 7,Aolefm of 2-subst. 1.3- butadienes, 7,Aolefin of electronically deactivated 1.3- butadienes ... 

Bromination of the enol ether product with two equivalents of bromine followed by dehydrobromination afforded the Z-bromoenol ether (Eq. 79) which could be converted to the zinc reagent and cross-coupled with aryl halides [242]. Dehydrobromination in the presence of thiophenol followed by bromination/dehydrobromination affords an enol thioether [243]. Oxidation to the sulfone, followed by exposure to triethylamine in ether, resulted in dehydrobromination to the unstable alkynyl sulfone which could be trapped with dienes in situ. Alternatively, dehydrobromination of the sulfide in the presence of allylic alcohols results in the formation of allyl vinyl ethers which undergo Claisen rearrangements [244]. Further oxidation followed by sulfoxide elimination results in highly unsaturated trifluoromethyl ketonic products (Eq. 80). 

A number of methods for the preparation of vinyl and allyl sulfones are available [1U9, 110], and the syntheses of vinyl sulfones from alkenes has been reviewed [116]. A simple one-step procedure of wide applicability makes use of a palladium-catalysed cross-coupling reaction between aryl and alkyl sulfonyl chlorides and substituted vinyl and allyl stannanes... 

The proton serves as the simplest electrophile to displace the silyl group stereo- and regioselectively. Numerous conditions have been used for the electrophilic protodesilylation of allyl- and vinylsilanes19. ( )-vinyl sulfones 2 are prepared from the silylallylic sulfones 1 in the presence of protic acids in high yield (equation l)34. Diastereoselective protodesilylation of allylsilane 3 gives 4 with excellent control of the geometry of the double bond exocyclic to the ring (equation 2)35. 

The epoxy-Ramberg-Backlund reaction (ERBR) has been used for the conversion of a,/3-epoxy sulfones into a range of mono-, di-, and tri-substituted allylic alcohols.34 Modification of this method has permitted the preparation of enantio-enriched allylic alcohols following the diastereoselective epoxidation of enantio-enriched vinyl sulfones that were accessed efficiently from the chiral pool. 

Inomata, K. Tanaka, Y. Sasaoka, S.-I. Kinoshita, H. Kotake, H. A convenient method for the preparation of a-alkylated vinylic sulfones and their conversion to allylic sulfones. Chem. Lett. 1986, 341—344. 

A sequential process involving a copper catalyzed cycloaddition of the vinyl sulfone 34 to Af-methylpropargylamine (35), and a subsequent palladium meditated allylic substitution, provided a route to mixtures of the separable isomeric pyrrolines 36 and 37 <02EJO1493>. 

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