Summary. New catalytic systems have been found which effect the isomerization of ccacetylenic alcohols to the corresponding a,P-unsaturated carbonyl compounds with high efficiency. These are combinations of silylvanadates with silanols or silanediols.u,p-Unsaturated carbonyl compounds, important intermediates in the manufacture of fragrances [l], carotenoids, and vitamins [Z] [6] and some contradictory reports [7]. Such rearrangements have been achieved by the use of a wide variety of acidic reagents [5] [6] [8] which often lead to complex mixtures of products. Meyer-Schuster RupsRearrangements of esterified acetylenic alcohols, however, proceed in high yield in the presence of certain transition metals [9] in charge induced [3s, 3s]-sigmatropic reactions [ l O j [ll], and the intermediates saponify cleanly to cr,P-unsaturated carbonyl compounds. Such a reaction has provided an important technical process for the manufacture of citral (2 $-3) from dehydrolinalool (1).

Zum Gedenken an Kml ZieglerDer Fortschritt auf dem Gebiet der homogenen Katalyse in den letzten funf bis sechs Jahren ist gekennzeichnet u. a. durch die Entwicklung hochselektiver Katalysatoren fur asymmetrische Synthesen. Mit wohldefinierten ubergangsmetallkatalysatoren lassen sich bei asymmetrischen Hydrierungen in hornogener Phase optische Ausbeuten von 85 bis uber 90% erzielen. Bei katalytischen Reaktionen, bei denen die chiralen Zentren i m Zuge von C-C-Verknupfungen entstehen, wurden optische Ausbeuten von 70 bis 80 % erreicht.Als Katalysatoren fur die Hydrierungen dienen vornehmlich Rhodium(1)-Komplexe rnit ,,Homer-Phosphanen", Phosphanen mit chiralen C-Atomen oder optisch aktiven Amiden. Fur die C-C-Verkniipfungen unter Induktion optischer Aktivitat haben sich Katalysatoren bewahrt, die aus n-Allylnickelhalogeniden, Lewis-Sauren und Phosphanen rnit chiralen C-Atomen gewonnen werden. Die Ergebnisse bedeuten einen Durchbruch auf einem Katalysegebiet, das bisher Enzymen vorbehalten war.

The progress made in the field of homogeneous catalysis during the last five to six years has led, inter alia, to the development of highly selective catalysts for asymmetric syntheses. Homogeneous asymmetric hydrogenation, using well defined transition metal catalysts, may be achieved with optical yields of 85 to 90% or more. Catalytic reactions, in which the chiral centers are generated by C-C bond formation, can result in optical yields of 70 to 80 YO. The hydrogenation catalysts consist primarily of rhodium(1) complexes containing "Horner phosphanes", phosphanes with chiral C atoms, or optically active amides. Catalysts which induce optical activity through the formation of C-C bonds have been developed from n-allylnickel halides, Lewis acids, and phosphanes containing chiral C atoms. The results obtained signify a breakthrough in an area of catalysis previously restricted to syntheses involving enzymes.