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Starting with natural monochiral (-)-(S)-2-methyl-l-butanolWith the new quaternary iminium salt 11, new monochiral (la) generated by alcoholic fermentations, we have synthesi-dinuclear tri-(13) and pentamethinium cyanine dyes (14) as zed the new monochiral heterocyclic iminium salt (+)-well as the trinuclear [2.2.2]heptamethinediium 17 and (3R,15S)-3-sec-butyl-1,2,3-trimethylindoleninium tetrafluo-[l.l.l]tetramethinium cyanine dyes 18 have been synthesiroborate (11) in an eight-step reaction sequence. Important zed. The absolute configuration of the four stereogenic censteps of this sequence are the zeolite-catalyzed Fischer syn-ters in the cyanine dye 14 has been confirmed by means of thesis of the monochiral indole 6a from the phenylhydrazone an X-ray structural analysis. Spectroscopical and chiroptical of ketone 5a and the separation of the diastereomeric salts 9 properties of all new cyanine dyes have been determined. and 10 by fourfold fractional recrystallization from ethanol.In addition to the well-known aromatic and polyenic TC systems, polymethine dyes constitute a third independent class of n:Their applications as so-called speciality or functional dyesr51 (i.e. as dyes with uses outside the conventional textile coloration field) include amongst others the use as dyes for the spectral sensitization of silver halide emulsions in as active or mode-locking substances in dye as possible material for nonlinear optics (i.e. for frequency doubling caused by second harmonic generation)L8], as dyes in sensor in devices for optical data storage['OI, as optical probes in membranes or model membrane systems ["], and as initiators in photopolymerizations[l2I. Surprisingly, chiral polymethine dyes with possibly interesting new chiroptical properties have only scarcely been studied up to now, in spite of the fact that some well-known polymethine dyes isolated from natural sources are indeed chiral pentamethine cyanine dyes: e.g. the orange-red fungus dye Muscaaurine I (from the toadstool fly agaric, Amanita muscaand the red-violet betalaine dye Betanine (responsible for the color of red beets, Beta vulgari~)['~I.The first artificial chiral polymethine dyes were synthesized by Konig and Langbein in 1928[15] and by Gotze in 1938[16]. We have recently repeated and improved the syntheses of Konig'~['~I and Gotze's[18] chiral polymethine dyes, and, in the case of Konig's dyes, we have for the first time determined their absolute configuration by means of X-ray structural analyses. In 1990, we realized the first synthesis of new chiral tri-and pentamethinium cyanine dyes with indolyl and quinolyl end groups and with known absolute configur a t i~n [~~,~~] .The absolute configurations of the stereogenic centers of these new dyes were known either by means of a crystal structural or because of the use of monochiral["l starting compounds with known absolute configuration such as (-)-(.S')-2-methyl-l-butanol[201, a side product of the alcoholic fermentation [22]. Very recently, an entirely different access to chiral pentameth...

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Syntheses and UV/Vis-spectroscopic properties of the chain-derivatives (5 and 6) of homochiral (S)-( +)-2-sec-Butylmalonsubstituted, homochiral pentamethine cyanine dyes 16 and 17 aldehyde (8), the first known chiral malonaldehyde, which in are described. 16 and l? as well as the homochiral five-, six-, turn is synthesized in a seven-step procedure from homochiral and seven-membered heterocycles 11 -15 are prepared from (Sj-( -)-2-methyl-l-butanol (1).Polymethinfarbstoffe, deren .n-Elektronensystem sich von dem der Polyene und der Aromaten deutlich abgrenzen 18Bt (Triadenprinzip von Dahne3)), haben nicht nur praktische Bedeutung als photographische Sen~ibilisatoren~) und Laser-Farbstoffe5), sie sind auch ideale Modellverbindungen zum Studium des Zusammenhanges zwischen Farbe und S t r u k t~r~~,~) .Um so erstaunlicher ist es, dal3 chirale Polymethine bisher kaum untersucht wurden, obwohl diese interessante chiroptische Eigenschaften haben sollten. Y O E t ____)

The synthesis of the unsymmetrical monomethine cyanine dye 6 in its monochiral (6a, b) and isochiral form (6c), first realized by Gotze in 1938, has been significantly improved and its spectroscopic properties have been studied. According to the synthetic pathway, the stereogenic center in dye 6 is delivered by monochiral 1-phenylethylamine.Polymethine dyes are not only important as spectral sensitizers in silver halide phot~graphy [~] and as laser dyed4], but also represent ideal 7c-systems for the study of correlations between structure and Surprisingly, chiral polymethine dyes with possibly interesting new chiroptical properties have been studied only scarcely up to now.Some natural dyes such as the red-violet betalaine dye Betanine (responsible for the color of red beets, Beta vulgaris) [6] and the orange-red fungus dye Musca-aurine I (from the toadstool fly agaric, Amanita muscaria)['I are known to be pentamethine cyanine dyes with chiral end groups stemming from L-a-amino acids. The first syntheses of artificial chiral polymethine dyes were described by Koniglsl in 1928 and by G o t~e [~] in 1938, however, the former only as a short report on a lecture given by Konig in Dresdenr81, and the latter only as a short communication with the remark that the work will be continued [9]. To the best of our knowledge, the work of both researchers in this field was not continued and published. Because of their historical importance, the sometimes insufficient elaboration of the synthetic procedures, the often unknown absolute configurations, and the possible applications of these chiral dyes, as well as in continuation of our recent work on synthetic chiral polymethine dyes['~lO], we[2.' '1 have repeated and significantly improved the syntheses of these dyes as first given by Konig[sl and G o t~e [~] .In this paper, we describe the synthesis and, for the first time, some spectroscopic properties of the monomethine cyanine dye 6 with a thiazolyl and quinolyl end group, following the work of GotzeL91. propionyl chloride and la, b, and 'H-and I3F-NMR spectroscopically investigated. From the integral NMR spectra it follows that the concentration of the minor diastereomeric Mosher amide amounts to ca. 2 cmol/mol, which corresponds to an e.e. value for la, b of ca. 96%. In the enantiomeric purity of the starting compounds la, b is not precisely given.