Naslov
Chiral 2-H Chromenes: Synthesis, Separation of Enantiomers and Barriers to Racemization

Autori
Lončar, Linda ; Otočan, Klaudio ; Mintas, Mladen ; Trötsch, Thomas ; Mannschreck, Albrecht

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Skup
XIII skup hrvatskih kemičara

Mjesto i datum
Zagreb, Hrvatska, 08.02.1993. - 10.02.1993

Vrsta sudjelovanja
Poster

Vrsta recenzije
Nije recenziran

Ključne riječi
kiralni kromeni; sinteza; odvajanje enantiomera
(chiral Chromenes; barriers to ring opening reaction)

Sažetak
Chromenes or 2H-benzopyrans have been the subject od extensive studies largely of their photochromic behaviour which consists in a reversible photoisomerization involving a rupture of the C (sp3) – O bond. In connection with our previous studies on 2, 2'-spirobichromenes1 we have prepared chiral chromeneses (l) and (2) in order to separate their enantiomers and determine the unknown barriers to ring opening reaction. The novel compounds (l) and (2) have been synthesized by reduction of the appropriate lactone with diisobutylaluminium hydride and subsequent O-alkylation of the resulting lactols. Separations or enrichments of enantiomers were achieved by liquid chromatography on triacetylcellulose and tribenzoylcellulose. (+)-(l) and (-)-(l) being separated almost completely, while in ( ± )-(2) an enrichment of enantiomers was achieved by using the recycling procedure. The barriers for reversible rin opening/ ring closure reaction of (l) and (2) were determined by thermal racemization of separated enantiomers (Scheme). The mechanism of interconversion of enantiomers necessarilly requires a ring opened dienone intermediate with a most probable Z-stereostructure (Scheme). Also, photochemically induced interconversion of preparatively isolated enantiomers of (+)-(l), i.e , photoracemization, was successfully performed for the first time in that class of chiral chromenes.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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