Hans Jörg Lindner

Initiation of polymerization with substituted ethanes—12. Free radical polymerization of methyl methacrylate and styrene initiated with 3-methoxycarbonyl-3-methyl-2,2,5,5-tetraphenylhexanedinitrile

Abstract The title compound, the first member of a homologous series of oligomers formed by free radical polymerization of methyl methacrylate initiated by tetraphenylbutanedinitrile, was synthesized and its structure was determined by X-ray diffraction. The longest CC bond of this molecule measures 1.628 A and can be thermally split to give radicals. The activation energy of this dissociation was found to be 150 kJ/mol. The kinetics of the free radical polymerization of methyl methacrylate and styrene initiated with the title compound shows remarkable deviations from the ideal polymerization kinetics, indicating that primary radical termination might be the main chain termination reaction.

Formal Asymmetric Synthesis of Pentalenolactone E and Pentalenolactone F-2. Construction of the Angular Diquinanoid δ-Lactone

A formal asymmetric synthesis of pentalenolactone E (1b) and pentalenolactone F (1a) has been accomplished. Ozonolysis of the diphenyl-substituted triquinane 3 and Kauffmann methylenation of ketone 5 with WOCl3-2 MeLi yielded the unsubstituted triquinane 9. The crucial rearrangement of the linear triquinanoid lactone 11 to the angular triquinanoid lactone 14a was accomplished using orthoformate and acid in methanol. Subjecting triquinanes 14a/b to the selenoxide method gave triquinene 15. Homologation of γ-lactone 15 to the angular diquinanoid δ-lactone 2 via a Horner-Wadsworth-Emmons or Peterson reaction of hemiacetals 16a/b was, however, not successful. Chemoselective reduction of 14a afforded hemiacetals 21a/b, reaction of which with the phosphonate salt 17a ultimately led to the ketene dithioacetal 22. The angular intermediates 25a/b were obtained from 22 by reduction to give the linear hemiacetals 24a/b, which rearranged to the dithio ortholactones 25a/b in the presence of acid. Introduction of the double bond and deprotection were accomplished via selenation of 25a/b with N,N-diethylbenzeneselenylamide and treatment of selenides 30a/b with silver nitrate. The unsaturated aldehydes 28 and 29 thus obtained were converted to 2 and 31, respectively, by oxidation with manganese dioxide in the presence of sodium cyanide, methanol and acetic acid. Alkene 2 was isolated by crystallization.

Aza-di-π methan-umlagerungen ?

Abstract 2,6-Diazabicyclo[3.2.o]hepta-2,6-dienes 3 are isolated as intermediates in the phototransformation of 4H-1,2-diazepines 1 to 6H-1,4-diazepines 4/5.★★)

Roseanolone: A New Diterpene from Hypoestes rosea

Abstract Roseanolone is a new diterpene from the African plant Hypoestes rosea (Acanthaceae). The isolation is described; the structure has been determined to be 1,2,3,3a,4,5,6,6a,7,8,9,10a-dodecahydro-5-hydroxy-3-isopropyl-3a, 6-oxa-6,9,10a-trimethyl-dicyclopenta[a,d] cycloocten-1-one by X-ray crystallography.