Substituted thian-4-ones. Part 3. Synthesis and reactions of 2-alkyl-5,6-dihydrothiin-4-ones

Kansal, Vinod K.; Taylor, Richard J. K.

doi:10.1039/p19840000703

Cited by 11 publications

(2 citation statements)

References 8 publications

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“…The desired compounds were prepared from the known p-ketoester 1 (15) according to Scheme 2.6 Alkylation (16) of 1 with 5-bromopentene (17) or 6-bromohexene (17) gave 2a and 2b, respectively, in modest yields along with products of 0-alkylation and ring fragmentation (18)-he decarboxylation of compounds such as 2 can be difficult (16b), and only a modest yield of 3 was obtained from 2 even using the recommended conditions (166). Dehydrogenation of 3 by reaction with N-chlorosuccinimide (NCS) according to the known procedure (19) proceeded with poor regioselectivity, as expected (20) Reactions in Schemes 2-4 were not optimized. Considerable literature precedent suggests that many of these transformations would proceed in high yield if conditions were optimized for the particular substrate.…”

Section: H-thiopyrans Had Established the 4-(triisopropylsilyl)oxymentioning

confidence: 97%

“…Presumably the 5-atom tether, the preference for an s-trans ester conformation (30), "' These compounds were very prone to elimination to give 56 and other by-products. ' I Chlorination under these conditions is precedented (20). propylsily1)oxy-2H-thiopyran with acrylate and crotonate dienophiles (7).…”

Section: H-thiopyrans Had Established the 4-(triisopropylsilyl)oxymentioning

confidence: 99%

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Intramolecular Diels–Alder reactions of 2H-thiopyran dienes

Ward¹,

Nixey²,

Gai³

et al. 1996

Can. J. Chem.

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Abstract:A systematic survey of IMDA reactions of 4-[tris(2-methylethyl)silyl]oxy-2H-thiopyran derivatives with potential dienophiles tethered at the C-2, C-3, C-5, and C-6 positions is presented. Cycloaddition was not observed with a C3 or C4 tether and an unactivated terminal olefin as dienophile. IMDA adducts could be obtained when dienophiles activated by a carbomethoxy group were employed. Compounds having the activated dienophile attached via a C3 tether to C-2 of the 2H-thiopyran gave adducts with high stereoselectivity. Substrates having the dienophile attached to C-3 with a C j or C, tether cyclized readily. With an (E)-enoate as the dienophile, the stereoselectivity was poor (endo:exo = 1.1-2.5: 1) and essentially independent of reaction conditions (i.e., thermal vs. Lewis acid mediated). With the (a-enoate, a 7: 1 mixture of enclo:e.ro IMDA adducts was obtained under thermal conditions; with Lewis acid catalysis, isomerization of the dienophile was competitive with cycloaddition. Type I1 IMDA adducts were not observed with C-5 tethered substrates. Compounds having the dienophile attached to C-6 via a C j or a five-atom tether also failed to give IMDA adducts. No evidence for isomerization of the 2H-thiopyran dienes by [1,5] sigmatropic rearrangement was observed. The etzclo adducts from IMDA reactions of the C-3 tethered substrates can be desulfurized to obtain synthetically useful trarzs-fused hydrindans and decalins with angular methyl groups.Key words: intramolecular Diels-Alder, 2H-thiopyran, cis-substituted 1,3-diene surrogate, trntls-octahydro-3a-methyl-IHindene derivatives, trcirls-decahydro-4a-methylnapthalene derivatives.RCsumC : On prCsente une Ctude des rCactions DAIM des dCrivCs du 4-[tris(2-mCthylCthyl)silyl]oxy-2H-thiopyrane avec des diknophiles potentiels attach& en positions C-2, C-3, C-5 et C-6. On n'observe pas de cycloaddition avec des laisses de 3 ou 4 atomes de carbone et une olCfine terminale dCsactivCe comme dienophile. Les adduits DAIM peuvent Ctre obtenus lorsque l'on utilise des dienophiles activCs par un groupe carbomCthoxy. Les composCs ayant le diCnophile attach6 par une laisse de 3 carbones attachCe au carbone en position 2 du 2H-thiopyrane donne des adduits avec une trks grande stCrCosClectivitC. Les substrats ayant un diCnophile attach6 en C-3 avec une laisse de 3 ou 4 atomes de carbone se cyclisent rapidement. Si on utilise un (E)-Cnoate conime diCnophile on obtient une faible stCrCosClectivit6 (et~clo : exo = 1,l-2,5 : I ) qui est independante des conditions de rCaction (c.-i-d., thermique versus une catalyse par acide de Lewis). Avec un (a-Cnoate on obtient un mklange d'adduits DAIM etlclo : eso dans la proportion de 7 : 1 par voie thermique tandis que la catalyse par un acide de Lewis conduit une compCtition entre I'isomCrisation du diCnophile et la cycloaddition. On n'a pas observe d'adduits DAIM de type I1 avec les substrats liCs en C-5. Les composCs ayant un diCnophile attach6 en C-6 via une liesse de 3 ou de 5 atomes de carbone ne donnent pas non plus d'adduits ...

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Section: H-thiopyrans Had Established the 4-(triisopropylsilyl)oxymentioning

confidence: 97%

Section: H-thiopyrans Had Established the 4-(triisopropylsilyl)oxymentioning

confidence: 99%