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Synthesis of Optically Pure Grasshopper Ketone and of Its Diastereoisomers and Related CompoundsStarting from our previously described synthon 1, the synthesis of four enantiomerically pure grasshopper ketons (diastereoisomeric 4-(2', 4'-dihydroxy-2', 6,6-trimethylcyclohexylidene)but-3-en-2-ons) and of their 0x0 derivatives was performed. Spectral and chiroptical data are presented.

Synthesis of (6R,all-E)-Neoxanthin and Related AUenic CarotenoidsWe present the first synthesis of enantiomerically pure neoxanthin (1) by a Witfig-Horner condensation between the ylide from the novel diethyl 12'-apo-15,15'-didehydroviolaxanthin-12'-phosphonate (35) and the allenic CI5-aldehyde 31 (Scheme 4 ) via the crystalline 15,15'-didehydroneoxanthin (36; 70% yield). After partial hydrogenation of the triple bond of 36 and isomerisation of the (152) is caused by a very easy thermal isomerisation into a mixture of the neochromes 4 and 5 (Scheme 1). Such a thermal rearrangement is not observed with 15,15'-didehydroneoxanthin (36). To explain this, we assume a zwitterionic excited state of the allenic group that induces the rearrangement of the violaxanthin end group into the furanoid epoxide (Scheme 7).

Synthesis of Enantiomerically Pure Mimulaxanthin and of Its (9Z,9'Z)-and (15Z)-IsomersWe present the details of a synthesis of optically active, enantiomerically pure stereoisomers of mimulaxanthin ( = (3S,5R, 6R,3'S,5'R,6'R)- 6,7,6',7'-tetradehydro-5,6,5',6'-tetrahydro-~,~-carotin-3,5,3',5'-tetrol) either as free alcohols l a and 24a or as their crystalline (t-Bu)Me,Si ethers l b and 24b. Grasshopper ketone 2a, a presumed synthon, unexpectedly showed a very sluggish reaction with Wittig-Horner reagents. Upon heating with the ylide of ester phosphonates, an addition across the allenic bond occurred. On the contrary, a slow but normal 1,2-addition took place with the ylide from (cyanomethy1)phosphonate but, unexpectedly, with concomitant inversion at the chiral axis. So a mixture of (6R,6S,9E,9Z)-isomers 6 9 was produced (Scheme I ) . However, a fast and very clean 1,2-addition occurred with the ethynyl ketone 12 to yield the esters 13 and 14 (Scheme 2). DlBAH reduction of the separated stereoisomers gave the allenic alcohols 15 and 16 in high yield. Mild oxidation to the aldehydes 17 and 18 followed by their condensation with the acetylenic C,,-bis-ylide 19 led to the stereoisomeric 15,15'-didehydromimulaxanthins 20 and 22, respectively (Schemes 3 and 4). Mimulaxanthins 1 and 24 were prepared by partial hydrogenation of 20 and 22 followed by a thermal (Z/E)-isomerization. As expected, the mimulaxanthins exhibit very weak CD curves, obviously caused by the allenic bond that insulates the chiral centers in the end group from the chromophor. On the contrary , some of the CIS-allenic synthons showed not only fairly strong CD effects but also a split CD curve which, in our interpretation, results from an exciton coupling between the allene and the C(9)=C(IO) bond. We postulate a rotation around the C(8)-C(9) bond, presumably caused by an intramolecular H-bond in 16 or by a dipol interaction between the polarized double bonds in 6, 7,8, and 17.1. Einleitung. ~ Mimulaxanthin ist ein sehr seltenes Carotinoid, welches bisher erst aus Bliiten von Mirnulus-Arten (Scrophulariuceae) [ 11 und Lamiurn montanum (Lamiuceue) [2] isoliert worden ist'). Seine Konstitution wurde von Nitsche hergeleitet [3]. Die absolute Konfiguration im Sinne von Formel l a (Schema I ) wurde von uns durch Ozonolyse der Di-0 -acetyl-Verbindung l c zum C,,-Allenketon 2a geklart [2].Seit langerem ist erkannt, dass die Allen-Endgruppe in Carotinoiden und deren Abbauprodukten in stereochemischer, biochemischer, synthetischer und spektroskopischer Hinsicht Probleme bietet, die heute erst zum Teil gelost sind*). Vor kurzem haben wir durch die Synthese der vier enantiomerenreinen C,,-Allenyl-ketone 2-5 einen weiteren Beitrag zu diesem Problemkreis geleistet [713). Die Verbindungen 2-5 sind von uns auch als Ausgangsmaterialien zur Synthese von Carotinoiden mit Allen-Endgruppen in Betracht gezogen worden.

The complexes of isolated benzoxazinone derivatives with Fe"' were investigated by means of electrospray ionization mass spectrometry. The hydroxamic-acid derivatives could be differentiated from the lactam or the methyl-hydroxamate derivatives by the formation of Fe"' complexes with two or three ligands. These complexes or adducts of them have been identified in the mass spectra. Moreover, the mass-spectral behavior of these complexes was not markedly influenced by the presence of a p -D-glucopyranosyloxy substituent.