26. Stereochemical studies of olefinic compounds. Part V. Further observations on the ring fission of 3-chlorotetrahydro-furans and -pyrans

Abstract

Chlorination of tetrahydrofuran and tetrahydropyran yields trans-2 : 3diclilorotetrahydrofuran and trans-2 : 3-dichlm-otetrahydropyran, identical with the compounds obained by adding chlorine to 2 : 3-dihydrofuran and 3 : 4-dihydropyran respectively. The configurations assigned to the two stereoisomers of the 2-alkyl-3-chlorotetrahydrofurans on the basis of the Auwers-Skita rules are supported by comparison of their speeds of dehydrochlorination with sodium ethoxide. Quantitative infrared analyses of the cis-Zrans mixtures of pent-3-en-1-01s and hex-3-en-1-01s formed on sodium ring fission of cis-and trans-3-chloro-2-methyl-and -ethyl-tetrahydrofurans are reported. Some reactions of 3-chlorotetrahydro-furans and -pyrans are reported.

Pathways for decomposition of THF by organolithiums: the role of HMPA

“…A similar reactions has been observed in a gas phase reaction between THF and hydroxide or amide ions, 14,15 and 5-endo-trig elimination of 3-metallated THF can be enforced by reaction of sodium with 3-chlorotetrahydrofuran. 16 During some studies of our dearomatising anionic cyclisation, [17][18][19] which until recently 20 involved a slow reaction with a t-BuLi-HMPA mixture, we too observed by-products consistent with the formation of 6 from THF, and in this paper we report the result of a brief study into the factors controlling which decomposition products are formed.…”

α-Amino carbene or carbenoid formation in the reaction of a tertiary amide with PhMe2SiLi and its insertion into the Si–Li bond of a second equivalent

“…As far as we are aware, the apparently simple E2 elimination from THF losing the proton from C-3 has not been seen before in solution chemistry, although it is thoroughly established with hydroxide ion and amide ion as bases in the gas phase, 10 and the formation of but-3-enol from the reaction between sodium and 3-chlorotetrahydrofuran is also known. 11 It is presumably unfavourable because the elimination is a retro-5-endo-trig reaction. We also found that the presence of a phenyl group in the N,Ndimethylbenzamide 14 stabilised the corresponding intermediate 15, which survived even at 220 °C, and gave a deuterated a-silyl amine 16 on quenching with D 2 O (Scheme 4).…”

Molécules modèles des motifs des poly-1,4-glucosides. I. Synthèse et correspondance configurationelle de diastéréoisomères avec les motifs de la cellulose et de l'amylose

“…dihydro-2,3 pyranne, prtpart par reduction du dimire de l'acroltine (35,36), prialablement acCtyle. L'hydrolyse finale de la fonction acetate, a froid en milieu basique, evite toute rupture possible de la liaison acCtal formte.…”

“…ComposPs 12,14-16 L'hydroxymethyl-2 dihydropyranne, prepart par reduction du dimere de I'acroleine (35,36), a kt6 acetyle selon la methode de Zelinski et a/. (36).…”