Nucleophilic substitution of p-3-trialkylsilyl-1,1-dimethyleneallyl palladium complexes 2a,b occurred on the carbon bearing the silyl group whatever the hard (hydride) or soft (malonate anion) nature of the nucleophiles. Conversely, when located on the cyclopropane ring, i.e., in b of the p-allyl palladium complex 12, the silyl group appeared able to overcome the ring strain effect and to direct the substitution on the three-membered ring. This effect was however reversed by the simultaneous presence of these two trialkylsilyl substituents on the p-allyl palladium complex 27. Electrophilic substitution of 1,1-dimethyleneallylsilanes 4a,b by benzaldehyde occurred regioselectively on the cyclopropane ring.Functionally substituted alkylidenecyclopropanes undergo readily in high yields inter-2 and intramolecular Pauson-Khand reactions, 3 as well as inter-4 and intramolecular 1,3-dipolar cycloaddition. 5 This reactive entity (SE = 40.9 kcal.mol -1 ) is however stable enough to be present in natural products which display powerful bioactivities. [6][7][8][9] As the presence of a silyl group was demonstrated to favour electrophilic substitution over simple addition to alkenes, 10,11 it appeared worthwhile to investigate the effect of s-donor and p-acceptor silyl groups 12 on the preparation and behaviour of silylated alkylidenecyclopropanes.It has been recently reported that the palladium(0) catalyzed hydrogenolysis of 1-(1-alkenyl)cyclopropyl esters, which are readily available from cyclopropanone hemiacetals, 13 constituted one of the most efficient preparation of alkylidenecyclopropanes 14 and offered an alternative to the Wittig reaction. 15 The regio-and diastereoselectivity of this new procedure, which allowed the first asymmetric synthesis of alkylidenecyclopropanes 15b appeared highly dependent on ring strain, substituents and phosphorus ligands steric effects. 16 Thus, hydrogenolysis of (E) 1-tosyloxy-1-(2-trimethylsilylethenyl)cyclopropane 1a (R=Me) 16 with sodium formate as hydride source in THF containing 10% of [15]-crown-5-ether, in the presence of 5% of palladium(0) [from Pd(dba) 2 -2 PPh 3 ] gave after stirring for 10 h at room temperature the (2-trimethylsilylethylidene)cyclopropane 4a, exclusively. Unsymmetric p-allyl palladium complex 2a with the palladium positioned closer to the cyclopropane moiety, i.e. on the allylic carbon bearing the least pronounced positive charge, as confirmed by high level calculations 5,17 and s-complex 3a arising from nucleophilic substitution by the formate anion were considered as intermediates to explain this unexpected high regioselectivity. Then, S Ni transfer of hydride with reductive Ln Pd(0) elimination and CO 2 extrusion led to 4a in 90% yield. 18 On the other hand, nucleophilic substitution of 2a by n-butylzinc chloride (from n-BuLi and ZnCl 2 ) provided in 85% yield, likely via the s-complexes 5a and 6a arising from b-elimination, the E-(2-trimethylsilylethenyl)cyclopropane 7a, exclusively. 18To overcome the problem resulting from the volatility of the 1,1-dime...

Die O‐Glycoside l des seco‐CI‐Derivats 2, das die seco‐Form der pharmakophoren Gruppe des cytotoxisch hochwirksamen Antibioticums CC–1065 ist, weisen nur eine sehr geringe Toxizität auf. In der tumorselektiven Krebstherapie können sie mit Konjugaten aus Glycohydrolasen und monoklonalen Antikörpern, die an tumorassoziierte Antigene binden, eingesetzt werden. Die Glycohydrolasen spalten die Prodrugs 1 unter Freisetzung der cytotoxischen Komponente 2.

No abstract