Sulfonates, cyclic, from allylic

More complex products are obtained from cyclizations in which the oxidizable functionality and the alkene are present in the same molecule. y9-Keto esters have been used extensively for Mn(III)-based oxidative cyclizations and react with Mn(OAc)3 at room temperature or slightly above [4, 10, 11, 15], They may be cyclic or acyclic and may be a-unsubstituted or may contain an a-alkyl or chloro substituent. Cycloalkanones are formed if the unsaturated chain is attached to the ketone. y-Lactones are formed from allylic acetoacetates [10, 11]. Less acidic /3-keto amides have recently been used for the formation of lactams or cycloalkanones [37]. Malonic esters have also been widely used and form radicals at 60-80 °C. Cycloalkanes are formed if an unsaturated chain is attached to the a-position. y-Lactones are formed from allylic malonates [10, 11]. yff-Diketones have been used with some success for cyclizations to both alkenes and aromatic rings [10, 11]. Other acidic carbonyl compounds such as fi-keto acids, /3-keto sulfoxides, j8-keto sulfones, and P-nitro ketones have seen limited use [10, 11]. We have recently found that oxidative cyclizations of unsaturated ketones can be carried out in high yield in acetic acid at 80 °C if the ketone selectively enolizes to one side and the product cannot enolize... 

Various terminal allylic compounds are converted into l-alkenes at room temperature[362]. Regioselective hydrogenolysis with formate is used for the formation of an exo-methylene group from cyclic allylic compounds by the formal anti thermodynamic isomerization of internal double bonds to the exocyclic position[380]. Selective conversion of myrtenyl formate (579) into /9-pinene is an example. The allylic sulfone 580 and the allylic nitro compound... 

An extensive review of 4 - - 3-cycloaddition reactions has been presented. The 1,3-difluorooxyallyl intermediate obtained from l-bromo-l,3-difluoropropan-2-one undergoes 4 + 3-cycloaddition with cyclopentadiene and ftiran to give difluorobicyclo[3.2.1]octenones. The use of 4 + 3-cycloaddition reactions of cyclic oxyallyls in the synthesis of natural products has been extensively studied. The intramolecular 4 + 3-cycloaddition of allylic sulfones (111) possessing a diene in the side-chain in the presence of Lewis acids yield cycloadducts (112) in good to excellent yields (Scheme 43). ... 

When the ferf-butoxycarbonyl (Boc) carbamate-derived sulfone 5 was subjected to the Bi(OTf)34H20-catalyzed allylation conditions (Scheme 2), the cyclic carbamate 6 was obtained as the major product (36%, diastereoisomeric ratio (dr) = 82 18), along with the corresponding allylation product 7, although in low yield (16%). Such cyclic carbamate resulting from the internal capture of an intermediate (3-silyl cation with the Boc group and concomitant loss of isobutylene has already been reported in the literature [59]. 

When favorable results in the case of allylic sulfones had been obtained, asymmetric synthesis of the cyclic sulfides 5a, 5ba, Sab and Sea (Scheme 2.1.4.9) and of the acyclic sulfides 6aa, Gab, 6ac, 6ba, and 6bb (Scheme 2.1.4.10) was investigated. As shown by Table 2.1.4.9, the pyrimidyl sulfide Saa could be obtained in medium to good yield (entry 1). Interestingly, the corresponding pyridyl sulfide Sab isolated from the reaction of rac-laa with 2-pyridinethiol had a much lower ee value (entry 2). The reaction of the cycloheptenyl carbonate rac-lba with 2-pyrimi-dinethiol afforded the sulfide Sba in a similar yield to the cyclohexenyl derivative... 

The Pd-catalyzed allylic alkylation of sulfinate ions, thiols, and thiocarboxylate ions with racemic cyclic and acyclic allylic esters in the presence of bisphosphane BPA generally provides for an efficient asymmetric synthesis of allylic sulfones, sulfides, and thioesters. The Pd-catalyzed rearrangements of allylic sulfinates and allylic O-thiocarbamates, both of which proceed very efficiently in the presence of BPA, are attractive alternative ways to the asymmetric synthesis of allylic sulfones and allyUc thioesters also starting from the corresponding racemic alcohols. 

The at complex from DIB AH and butyllithium is a selective reducing agent.16 It is used tor the 1,2-reduction of acyclic and cyclic enones. Esters and lactones are reduced at room temperature to alcohols, and at -78 C to alcohols and aldehydes. Acid chlorides are rapidly reduced with excess reagent at -78 C to alcohols, but a mixture of alcohols, aldehydes, and acid chlorides results from use of an equimolar amount of reagent at -78 C. Acid anhydrides are reduced at -78 C to alcohols and carboxylic acids. Carboxylic acids and both primary and secondary amides are inert at room temperature, whereas tertiary amides (as in the present case) are reduced between 0 C and room temperature to aldehydes. The at complex rapidly reduces primary alkyl, benzylic, and allylic bromides, while tertiary alkyl and aryl halides are inert. Epoxides are reduced exclusively to the more highly substituted alcohols. Disulfides lead to thiols, but both sulfoxides and sulfones are inert. Moreover, this at complex from DIBAH and butyllithium is able to reduce ketones selectively in the presence of esters. 

Allylic trichloroacetimidates, generated in situ from cyclic y-hydroxy-a,P-unsaturated sulfones, undergo intramolecular conjugate addition to the vinyl sulfone moiety to afford oxazolines. Acid hydrolysis of the oxazolines generated... 

Five-membered, cyclic allylic sulfones, except the parent 2,5-dihydrothiophene 1,1 -dioxide, underwent smooth addition of dichlorocarbene generated from chloroform/base/phase-transfer catalyst giving 4. ... 

From the constitutional point of view, the employment of formic acid leads to interesting results, since hydride is site selectively transferred to the more hindered position of the allylic sulfone (Eq. 45).89 Thus, a hydride equivalent generated from formic acid is exceptional in this respect. It is proposed83 that decarboxylation and hydride transfer is a concerted process in which the hydride site selectively attacks the more substituted (more electropositive) side of the allylic system in a cyclic mechanism (SNi transfer of hydride, Scheme 1). 

Sulfones are also useful as allylic leaving groups in palladium-mediated alkylations. In particular cyclic 2-sulfonyl-l, 3-dienes, which are readily available from a one-pot sulfonylmercura-tion/elimination of 1,3-dienes, are versatile starting materials107. The palladium-catalyzed substitution of allyl sulfones occurs with net retention of configuration and features attack on the least substituted 7i-allyl terminus108. 

Cycloaddition of allyl cations to conjugated dienes provides a route to seven-membered carbocycles. One of several methods can be used to generate the allyl cation, such as from an allyl halide and silver trifluoroacetate, or from an allyl alcohol by way of its trifluoroacetate or sulfonate. Cycloaddition of the allyl cation proceeds best with a cyclic diene, particularly for intermolecular reactions. Thus, cyclohexadiene and methylallyl cation gave the bicyclo[3.2.2]nonadiene 187 (3.125). Many intramolecular examples are known, such as the formation of the... 

The use of sulfonates as nucleophiles as a method to form enantiomerically enriched allyl sulfones was first reported by Hiroi and Makino in 1986.Acyclic allyl sulfones have been prepared from substrates 4 and 188 under the control of phosphino-oxazoline ligands 29 (R = Ph) ] or Trost ligand 20. 531 The reaction has also been applied to cyclic substrates including carbonate 191 (Scheme 39).B5 ]... 

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