1.3- Diene monoepoxides

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

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>. 

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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