Showing papers on "Claisen rearrangement published in 1968"

Stereochemie des Übergangszustandes aliphatischer CLAISEN‐Umlagerungen. Vorläufige Mitteilung

Abstract: The stereochemistry of the transition state in the CLAISEN rearrangement of crotyl propenyl ethers (2) has been established. By heating trans, cis-, cis, cis- and trans, trans-crotyl propenyl ether at 142,5°, erythro and threo 2, 3-dimethylpent-4-en-1-al (3 and 4) were obtained. From the ratio 3/4 it was shown that the rearrangement of the three ethers largely involves (97–98%) a chair-like transition state.

Thermische Umwandlung von Phenyl‐penta‐2,4‐dienyläthern in 4‐[Penta‐2,4‐dienyl]‐phenole als Beispiel für [5,5]‐sigmatropische Umlagerungen. Vorläufige Mitteilung

Abstract: The reaction between phenol and trans penta-2,4-dienyl chloride gave trans penta-2,4-dienyl Phenyl ether (I), whereas with a mixture of sorbyl chloride and 1-methylpenta-2,4-dienyl chloride, pure trans, trans hexa-2,4-dienyl phenyl ether (IV) and trans 1-methylpenta-2,4-dienyl phenyl ether (V) were obtained. The ether I gave, on heating in dilute solution at 185°, 4-(penta-2,4-dienyl)-phenol (III) as the main product, and also some 2-(2-vinylallyl)-phenol (II). The ether IV provided, on heating at 165°, in addition to the ortho CLAISEN rearrangement product VI, mainly a mixture consisting of 94% 4-(1-methylpenta-2,4-dienyl)-phenol (VIII) and only 6% 4-(hexa-2,4-dineyl)-phenol(IX). The latter product (IX) was the only para isomer produced on heating ether V, but in addition 22% of the ortho rearrangement product VII was formed. The migrations I III, IV VIII, and V IX, proceeding through a ten membered transition state, are the first [5,5] sigmatropic rearrangements described.

The synthesis of (±)-bakuchiol

Abstract: The synthesis of the racemate of the naturally occurring phenol, bakuchiol, p-(3,7-dimethyl-3-vinylocta-trans-1,6-diimyl)phenol, is reported. The key step was the in situ formation and Claisen rearrangement of the geranyl enol ether of acetophenone to 1-p-methoxyphenyl-3,7-dimethyl-3-vinyloct-6-en-1-one (IIIa). Bakuchiol cyclised readily in the presence of acid.

Polymerization of allyl(vinyl phenyl) ethers and reactions of the resulting polymers

Abstract: Solution polymerizations of allyl(o-vinyl phenyl)ether and allyl(p-vinyl phenyl)ether with cationic and radical initiators were investigated. Soluble polymers were formed in polymerizations with boron trifluoride etherate and with benzoyl peroxide. In polymerization with azobisisobutyronitrile the polymerization in dilute solution gave a soluble polymer, whereas that in concentrated solution gave a crosslinked, insoluble one. For informationon the polymerization behavior some infrared and ultraviolet spectroscopic investigations of the soluble polymers were made. From these results it appears that polymers with pendant allyl groups are formed in polymerization with boron trifluoride etherate at low temperature, and polymers containing pendant vinyl groups and allyl groups are obtained with the two types of radical initiator. Copolymerizations of these monomers with ethyl vinyl ether and styrene with the use of boron trifluoride etherate were sucessfully effected. Such reactions as Claisen rearrangement, crosslinking induced with radical initiators, and epoxidation with perbenzoic acid were examined for the polymers prepared in the polymerization with boron trifluoride etherate. Good results were obtained for the former two reactions. However, the latter was unsuccessful.