Stereoselective Mannich-type reaction of chiral aldimines with 2-silyloxybutadienes by using trifluoromethanesulfonic acid

Novel stereoselective Mannich-type reaction of chiral aldimines with 2-silyloxybutadienes in the presence of trifluoromethanesulfonic acid has been carried out to give the corresponding products, which are not obtained by general Lewis acid-promoted methods, with 70-92% de in 62-74% yield. No cycloadducts were detected in the crude product by ¹H NMR.     

Synthesis of oxiranes based on 1,1,2,3,3-pentafluoro-1,5-hexadiene

Interaction of 1,1,2,3,3-pentafluoro-1,5-hexadiene with Br₂ in a MeCOOH medium results in the product of selective bromination of the hydrocarbon double bond,i.e., 5,6-dibromo-1,1,2,3,3-pentafluoro-1-hexene. Epoxidation of the latter with H₂O₂ in an alkaline medium followed by debromination afforded 5,6-epoxy-4,4,5,6,6-pentafluoro-1-hexene for the first time.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1530–1533, August, 1995.     

Metathetic alkenolysis of unsaturated units in polymers and copolymers--application to the synthesis of epoxy-functionalized oligomers and organic compounds

Depolymerization of 20% epoxidized cis-1,4-polybutadiene was carried out through alkenolysis of the butadiene repeat units (B) using 4-octene as depolymerizing agent (DA) and bis(tricyclohexyl phosphine)benzylidene ruthenium (IV) dichloride (1) as catalyst. The average molecular weight of the depolymerization products was determined by NMR, and SEC, and their constituents were identified by GC MS. Cis-4-octene was found more efficient in performing the depolymerization as compared to its trans isomer. Besides dodeca-4,8-diene and hexadeca-4,8,12-triene, 2,3-di[3-heptenyl]-oxirane with a cis oxirane configuration was clearly characterized. Beside the DA to B mole ratio, the catalyst to double bond mole ratio was observed as the major factor controlling the molecular weight of the depolymerization products and the 2,3-di[3-heptenyl]-oxirane yields.     

Reactivity of unsaturated sultones synthesized from unsaturated alcohols by ring-closing metathesis. Application to the racemic synthesis of the originally proposed structure of mycothiazole

Unsaturated sultones have been synthesized from various primary or secondary alkenols by ring-closing metathesis of the corresponding unsaturated sulfonates. By treatment with a strong base, β,γ-unsaturated sultones can be metalated and subsequently alkylated with electrophiles. When iodomethylmagnesium chloride was selected as the electrophile, seven-membered ring β,γ-unsaturated sultones were converted into homoallylic conjugated (Z)-dienols. This methodology was applied to the racemic synthesis of the originally proposed structure of the marine natural product mycothiazole.     

FeCl3-Mediated Reaction of 1,4-Dilithio-1,3-dienes with Alkynes Affording Benzene Derivatives

Unactivated alkynes reacted with 1,4-dilithio-1,3-diene derivatives in the presence of FeCl3 affording substituted benzene derivatives via a formal[4 2] cycloaddition.     

An efficient synthesis of dienic nucleoside analogues via a Mitsunobu reaction

Nucleoside analogues 9 and 12 were obtained in good yields from alcohol 7 which, under Mitsunobu conditions, led to the title products after deprotection steps.     

Fast diastereoselective Baylis-Hillman reaction by nitroalkenes: synthesis of di- and triene derivatives

The Baylis-Hillman reaction is performed using nitroalkenes as activated alkenes, ethyl-2-bromomethylacrylate as electrophilic acceptor and DBU as catalyst base. Nitro dienes are obtained in good yields and very short reaction times. Moreover, starting from appropriate nitroalkenes it is possible to realize one pot the synthesis of trienic systems.     

Spirodialkylation of 3-(Phenylthio)-3-Sulfolene and Subsequent Synthetic Transformations

3-(Phenylthio)-3-sulfolene (1) underwent spirodialkylation to give products 2 which were desulfonylated to afford the dienes 3. The Diels-Alder reaction of 3 was achieved for some reactive dienophiles to yield spiro compounds. Compounds 2 were also converted to sulfonyldienes 9 which reacted as Michael acceptors.     

The Diels-Alder Reaction of Dienes Derived from Substituted 3-(Phenyl-Thio)-3-Sulfolenes

Substituted 3-(phenylthio)-3-sulfolenes (3) and (4) are good precursors for 2-(phenylthio)-1,3-butadienes (5) and (6). The Diels-Alder reaction of the dienes derived from (3) and (4) with various dienophiles was studied. It was found that heating of sulfolenes (3) with methyl propiolate and N-phenylmaleimide afforded the Diels-Alder adducts of (5) directly and with complete regio- and stereospecificity. The same reaction with methyl vinyl ketone gave a mixture of endo and exo addition products. If sulfolenes (3) were first converted to the dienes (5) using lithium aluminum hydride and then reacted with methyl vinyl ketone in the presence of anhydrous zinc chloride, the stereoselectivity could be improved. Sulfolenes (4) also underwent cycloreversion/cycloaddition with methyl acrylate, methyl vinyl ketone, and N-phenylmaleimide, but gave mostly the double bond-isomerized cycloaddition products. The regiochemistry of cycloaddition was delicately dependent on the dienophiles used.