Monoepoxidation diene

Cu(i(-catalyzed kinetic resolutions of racemic, cyclic 1,3-diene monoepoxides through the use of dialkylzinc [123] or trialkylaluminium reagents [124] have re-... 

Zinc homoenolate reacts with allylic halides and diene monoepoxides under copper catalysis [29]. Treatment of the zinc nomoenolate with a catalytic amount of Cu(II) in a polar solvent (e.g. hexamethylphosphoramide, HMPA, N,N-dimethylacetamide, DMA) generates a copper species which undergoes clean Sn2 allylation reactions Eq. (40). Polar solvents not only accelerate the reaction but greatly improve the SN2 selectivity. A variety of allylating reagents can be employed in this reaction (Table 9). The SN2 /SN2 ratio is particularly high (close to 100%) when the alkylated carbon bears no substituents. The reaction of... 

The effects created by these functionalities are, surprisingly, capable of being transmitted from positions even more remote to the allyl ligand. 1,3-Diene monoepoxides, for example, selectively undergo the addition of nucleophiles remote from the incipient hydroxymethyl group (equation 220).410 4 3 Nitro 414 malonate415 and acetoxy416,417 functionalities show similar tendencies (equations 221-223). Tri-... 

Reaction of RCHO with 1,3-diene monoepoxides.4 The monoepoxides of butadiene or of isoprene after treatment with CrCl2 and 1A1 (2 l) react with aldehydes to form cis-l,3-diols with a quaternary center at C2. 

An unusual syn addition to epoxides occurs when 1,3-diene monoepoxides are treated with organozinc reagents. Thus, the cyclic vinyl epoxide 72 was converted to the cis-ethyl-cyclohexenol 75 with diethyl zinc in methylene chloride and trifluoroacetic acid. The syn addition is believed to derive from an initial coordination of the oxiranyl oxygen to the organozinc compound, which then delivers the alkyl group to the same face. This transfer is facilitated by a relaxation of the sp3 hybridization brought about by the Lewis acidic zinc center and the allylic character of the incipient carbocation <020L905>. 

An example that used this protocol the substrate of which contains a sensitive functionality is depicted in Scheme 45 [202]. 1,3-Diene monoepoxide is easily attacked by a palladium(O) complex to form the corresponding 7r-allylpalladium species. Thus such a process could be banished from the desired selective transformation as depicted in Scheme 46 by the employment of the alkynyltin reagent with an aid of triphenylarsine ligand [203]. Organotin protocol is also convenient for introduction of a small alkynyl moiety such as C2 or C3 or preparation of symmetrical diarylethynes (Scheme 47) [204]. Shirakawa et al. reported recently that iminophosphine 4 is much more effective ligand for palladium than tris(2-furyl)phosphine in this reaction (Scheme 48) [32,205]. 

Xue et al. have found that otganozinc reagents (ZnEt2, ZnPh2) react with cyclic 1,3-diene monoepoxides in the presence of CF3COOH to give the s-addition products (Scheme 34) <20020L905>. 

Samarium iodide is a reagent capable of highly selective reduction of epoxy ketones and esters to the corresponding alcohols (Table 12). Diene monoepoxides are converted with high regio- and stereo-selectivity to the ( )-allylic alcohols, and the reaction can be carried out at -90 C under neutral conditions. As a result functional groups such as alkoxycarbonyl, carbonyl and cyano survive. 

Conacher and Gunstone reported the novel conversion of the diene monoepoxide methyl vemolate (187 equation 78) to the cyclopropyl keto isomer (188). Later Italian work supported this conclusion, and furnished additional examples of cyclopropane formation. 

An organoaluminum compound in hydrocarbon solvent caused rearrangement of an acid-sensitive diene monoepoxide, but a change to ether solvent mediated this (undesired) reaction. 

Ring Contraction of Cycloocta-1,4-diene Monoepoxide and in situ Generated Cyclooctanylidenes... 

The carbonate anion loses C02 to give methoxide ion which, like the anion released from a diene monoepoxide, is basic enough to deprotonate the nucleophile, a bis-sulfone 296. The anion from this 295 adds to the less hindered end of the allyl cation complex 294. The product 297 has the skeleton of the prostacyclin analogue and the sulfones simply need to be removed by reduction. 

Aq. NaN3 and a soln. of startg. vinyl epoxide in THF successively added dropwise with stirring under N2 to a little Pd(PPh3)4 in the same solvent, and stirred at room temp, for 5-10 min - product. Y 75% synsantil 1). Cyclic 1,3-diene monoepoxides failed to react there was moderate diastereoselectivity with carbohydrate derivs. F.e.s. A. Tenaglia, B. Waegell, Tetrahedron Letters 29, 4851-4 (1988). 

An alternative approach for achieving enantiodivergence from aUyHc C—O containing substrates is illustrated in the copper-catalysed reaction of 1,3-diene monoepoxides with dialkylzinc reagents (Scheme 6.22) [42]. For the reaction of rac-98 with dimethylzinc in the presence of the chiral phosphoramidite ligand... 

Pd-catalyzed cyclizations of 1,3-diene monoepoxides have thoroughly been studied due to their powerful applications in the total synthesis of natural products such as steroid precursors, vitamin intermediates, or 3-lactone moieties. For example, diastereo- and re-gioselective cycloisomerization of a diestervinyloxirane leads to the 3-lactonic precursor of Cholestane (Scheme 13). 

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