No abstract

For the transfer of the cyanomethyl residue with high alde-the aldehyde-vs. ketone-selective transfer of the branched hyde vs. ketone selectivity, the Fe reagent 3a is a good alter-residues 1-cyanoethyl and cyanoisopropyl, the Fe reagents 3b native to the known Ti reagent la['], whereas analogous reand 3c are distinctly better than the Ti reagents l b and l c . agents with the metals Mn, Co, Ni or Cu are unfavorable. For

In intermolecular competition experiments with substrate group. For the anticheleselective transfer of the cyanoisopropairs which consist of a 0-functionalized ketone and a normal pyl group, NC -CMezFeCl (3 b) is superior to the correspondketone, cyanoalkyl derivatives of Fe, Ti, Cr, and Mn prefer in ing Ti reagents. The ability of 4a as a highly anticheleselective every case the normal ketone (..anticheleselectivity"). NC-cyanomethylating reagent has also been demonstrated with CH,Ti(OiPr)3 (4a) and NC -CHzFeCl (3a) are the best rea-an intramolecular competition system (diketone 13). The reagents for the anticheleselective transfer of the cyanomethyl sons for the observed anticheleselectivity are discussed. Ob mit Cyanoalkyl-Ubergangsmetall-Reagenzien, von denen einige sehr gut zwischen Aldehyd-und Ketogruppen unterscheiden konnen['], auch eine Differenzierung zwischen verschiedenartigen Ketogruppen gelingt, ist eine interessante Frage. Wichtig ist dabei auch der Vergleich rnit der Selektivitat und Reaktivitat der elektronisch ahnlichen Allyl-Ubergangsmetall-Reagenzien, da bei Umsetzungen von Allylderivaten der Metalle Ti [233a1, Cr [233b1, V[2*3c1 und Fe[3d1 rnit Konkurrenzsystemen, die aus einem funktionalisierten Keton und einem normalen Keton bestehen, Anticheleselektivitat [21, d. h. bevorzugte Allylierung des normalen Ketons, beobachtet worden war. A) Inter-und intramolekulare Konkurrenzurnsetzungen'3e' a) P-MethoxyketonJKeton-Konkurrenz: Da keine Erfahrungen daruber vorlagen, ob Cyanoalkyl-Ubergangsmetall-Reagenzien zwischen verschiedenen Ketogruppen differenzieren konnen, wurde zunachst eine Serie solcher Reagen-NC-C R, [ MI 0 OMe 0 T H F , -7O'C bis R:H,Me P h K / + PhK rnoglichst quantitativen Cyanoalkylierung basenempjindlicher Ketone rnit schwach basischen Ubergangsrnetall-Reagenzien: Chem. Ber. 1992, 125, 907 -912 0 VCH Verlagsgesellschaft mbH, D-6940 Weinheim, 1992 0009 -2940/92/0404-0907 $ 3.50+ .25/0

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.