Enantio‐ and stereoselective cyclopolymerization of hexa‐1,5‐diene was achieved by enantiomerically pure dichloro zirconium(IV) pre‐catalysts 2 possessing chiral [OSSO]‐type bis(phenolate) ligands (−)‐ 1 and (+)‐ 1 in combination with dried methylaluminoxane (dMAO) as an activator. The corresponding activities were recorded with quite high values up to 1,960 g mmol( 2 )–1 h–1, which are extremely larger than those of the related complexes. The microstructure analysis for the PMCPs furnished by pre‐catalysts (Λ,S,S)‐ 2 and (Δ,R,R)‐ 2 showed good isotacticity factors (α = 75−78%) and relatively high proportions of trans‐cyclopentane rings (σ = 14−21%). These enantiomeric PMCPs exhibited large specific optical rotations ([α]D = +28 to +32° from (Λ,S,S)‐ 2 , −26 to −34° from (Δ,R,R)‐ 2 ).
DNA hybrid catalysis goes organometallic : A DNA strand functionalized with diene ligands forms iridium(I) complexes that can efficiently catalyze an allylic amination in aqueous medium (see scheme). The DNA‐based complexes show high stability and activity, and their secondary structure influences the stereoselectivity of the reaction.
A plan for enantioselective construction of the mangicol A framework by means of intramolecular Diels-Alder cycloaddition is outlined. First to be assembled is the enantiopure cyclopentenecarboxylic acid 16. Of the several approaches targeting the 1,3-diene component 56, only that involving palladium-catalyzed enyne cyclization proved successful. Following the coupling of 16 to 56, we were unable to bring about any detectable level of (4π+2π) cycloaddition. Activation of the diene by incorporation of an OSiEt3 substituent on a terminal sp2-hybridized center likewise proved unsuccessful. Further facilitation was sought in the form of cyclopentenonecarboxylate 66. However, thermal activation, Lewis acid catalysis, and high-pressure conditions proved ineffective and did not lead to C-C bond formation. These studies serve to underscore the extent to which steric complications can complicate matters and the extent to which they must be skirted to arrive at the title compound. 相似文献
Upon heating in DMF medium with KF and 18-crown-6 1,1,2,2,3-pentafluoro-1,5-hexadiene (1) is converted to 4,5,6,6,6-pentafluoro-1,3-hexadiene and 1,1,1,2,3-pentafluoro-2,4-hexadiene. Reaction of (1) with KHF2 results in the formation of its HF addition product, namely, 4,4,5,6,6,6-hexafluoro-1-hexene. We assume that the driving force in the isomerization of (1) is the formation of conjugated products, involving both the fluorinated and nonfluorinated portions of the molecules, preferably with the minimum number of fluorine atoms attached to the double bond.Department of Fine Organic Synthesis, Institute of Organic Chemistry, Ural Branch, Russian Academy of Sciences, 620219 Sverdlovsk. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 2, pp. 408–411, February, 1992. 相似文献
Reaction of [(3-C4H7)2Rh(CH3CN)2]PF6(3-C4H7 = -methallyl) with [n-Bu4N](VO3) gives a new 3-allyl cluster [n-Bu4N]2[{(3-C4H7)2Rh}2 (V4O12)] (I) which is readily converted into a diene cluster, [n-Bu4N]2 [{(4-C8H14)Rh}2(V4O12)] (II) (C8H14=2,5-dimethyl-1,5-hexadiene) by reacting with CO or P(OEt)3;I andII have been characterized crystallographically. 相似文献