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Aromatic thallation is shown to be a reversible, electrophilic substitution reaction with an energy of activation of 27 kcal/mol and a large steric requirement. The process of thallation followed by addition of aqueous potassium iodide represents a simple and facile synthesis of aromatic iodo compounds, and the factors (kinetic, thermodynamic, steric) which control the position of thallation (and hence of iodination) have been systematically explored. Meta substitution is achieved under conditions of thermodynamic control. Under conditions of kinetic control, ortho substitution results when chelation of the reagent (thallium(III) trifluoroacetate, TTFA) with the directing substituent permits intramolecular delivery of the electrophile, and para substitution results when such capabilities are absent. Thus appropriate manipulation of conditions can lead to control over orientation (ortho or meta or para) in the same electrophilic substitution reaction. The application of these observations to the selective synthesis of a number of aromatic iodo compounds is described.

Herrn Professor Dr. Walter Bogurh zum 60. Geburtstag gewidmet (10.111. 77) lH-NMR., 13C-NMR., UV. and CD. spectral data of synthetic (3S, 3's)-astaxanthin, its 15-cis isomer, and some related compounds Summary 1H-NMR., 13C-NMR., UV. and CD. spectra are reported for synthetic (3 S, 3's)-astaxanthin (l), its 15-cis isomer (2), its diacetate (3), and the 15,15'-didehydro compound (5). These data prove the identity of the synthetic and the naturally occuring compound 1. A full interpretation of the lH-and 13C-NMR. spectra is given and confirms the configuration of all the double bonds. The conformation of the cyclohexene end group of all the compaunds is shown to be identical. The signs of the different CD. maxima of 15-cis-astaxanthin are found to be opposite to those of the all-trans compound.Einleitung. - Obwohl das Vorkommen von Astaxanthin sehr oft in der Literatur erwahnt wird, geschieht dessen Nachweis meist nur durch UV.-und Massen-Spektroskopie. Da haufig freies Astaxanthin und dessen Mono-und Di-ester nebeneinander anzutreffen sind, erfolgt deren gemeinsamer Nachweis in vielen Fallen spektroskopisch sogar erst

Nucleophilic alkylation of aromatic nitro compounds SummaryAromatic nitro compounds may be alkylated in o-or p-position by treatment with alkyl lithium or alkyl Grignard reagents.

The possibility to functionalize selectively various polyenes using hydroboration or a Vilsmeyer‐type formylation was demonstrated. Reversible sulfur dioxide addition may be used in some cases to protect two double bonds in a polyene system. Reactions with mercuric acetate, thallium(III) nitrate, bromine or peracetic acid were found useful only in some cases for the selective introduction of functional groups.

Synthesis of Optically Active Natural Carotenoids and Structurally Related Compounds. VIII. Synthesis of (3S,3′S)‐7,8,7′,8′‐Tetradehydroastaxanthin and (3S,3′S)‐7,8‐Didehydroastaxanthin (Asterinic Acid) The synthesis of all‐trans‐(3S,3′S)‐3,3′‐dihydroxy‐7,8, 7′,8′‐tetradehydro‐β, β‐carotene‐4,4′‐dione (1), of all‐trans‐(3S,3′S)‐3,3′‐dihydroxy‐7, 8‐didehydro‐β,β‐carotene‐4,4′‐dione (2) (asterinic acid = mixture of 1 and 2), and of their 9,9′‐di‐cis‐ and 9‐cis‐isomers is reported starting from (4′S)(2E)‐5‐(4′‐hydroxy‐2′, 6′,6′‐trimethyl‐3′‐oxo‐l′‐cyclohexenyl)‐3‐methyl‐2‐penten‐4‐ynal (8). The absolute configuration (3S,3′S) for both components 1 and 2 of asterinic acid ex Asterias rubens is confirmed on the basis of spectroscopic and direct comparison.