Allylic monoepoxide

Carboxylate anions are better nucleophiles for allylation. The monoepoxide of cyclopentadiene 343 is attacked by AcOH regio- and stereoselectively via tt-aliylpalladium complex formation to give the m-3,5-disubstituted cyclopen-tene 344[212]. The attacks of both the Pd and the acetoxy anion proceed by inversion (overall retention) to give the cis product. 

Moreover, Pd(0)-catalyzed allylations of imidazole with cyclopentadiene monoepoxide led to imidazole-substituted cyclopentenol in moderate yield [54],... 

A recently described method for insertion of a carbon monoxide molecule into the monoepoxide of a conjugated diene gives /3-lactones in high yield. This is achieved by reaction of iron pentacarbonyl with the starting vinyloxirane to give the 7r-allyl iron complex (66), which on oxidation with cerium(IV) ammonium nitrate gives the /3-lactone. In some cases, y-Iactone products can also be obtained from this reaction (8lJCS(Pi)270). 

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-... 

The exceptionally facile epoxidation of allylic alcohols by tert-butyl hydroperoxide in the presence of vanadium catalysts, discussed earlier, has been used466,467 for the synthesis of complex molecules. Thus, geraniol (X) and linalool (XI) are selectively epoxidized to the previously unknown monoepoxides with f-Bu02 H-V 0(acac)2 466 ... 

Fig (22) 2-isopropylphenol (183) is converted to allylic alcohol (185). Its bromide derivative reacts with methyl acetoacetate. The resulting compound undergoes radical cyclization yields ketoester (186) whose vinyl triflate on reduction and carbonylation furnishes lactone (187). Diol (188) obtained from (187), is converted to monoepoxide (189) which on further epoxidation produces triptonide (148). Its conversion to triptolide (149) is accomplished by reduction. 

The conversion of racemic butadiene monoepoxide to a single enantiomer of 54 (R=CH2OH) using Pd-catalyzed asymmetric allylic alkylation was uncovered by Trost [141]. By using a slightly modified ligand, the alkylation with phthalim-... 

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>. 

The /J-adduct is formed from (5Z)-cholecalciferol by attack from above the plane of the molecule (i.e., anti to the hydroxy substituent). In fact, by assuming the endo mechanism for cycloaddition, no steric influence should be exerted by the C-18 methyl and side chain substituents. The opposite configurations were originally assigned to the adducts 127, but this was later corrected after X-ray analysis the correct assignments are shown in the diagram9. Monoepoxides, and in turn allylic alcohols, have been furthermore prepared from the adducts 1210. 

Trost has reported enhanced enantioselectivity in the desymmetrization of mero-biscarbamates in the presence of triethylamine. Under these conditions, high yields (>80%) and enantiomeric excesses (93-99% ee) are obtained. This methodology has been applied to the synthesis of (—)-swainsonine. a-Amino esters have been used as nucleophiles in the reaction with acyclic allylic esters and isoprene monoepoxide, providing access to diastereoselective N-alkylated a-amino esters. By employing the feature ligand, asymmetric palladium(0)-catalyzed cychzation of 2-(tosylamino)phenol with ( -l,4-bis[(methoxycarbonyl)oxy]but-2-ene provides 2-vinylbenzomorpholine in 79% ee. A number of alternative diphosphine ligands were studied and found to be inferior. 

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. 

The other question is why work at low temperature and buffer the solution The low temperature favours the kinetic product and discourages the slower second epoxidation. A by-product from epoxidation is the acid RCO2H and there is a danger that this may catalyse opening of the monoepoxide to give the allyl cation in the frame. A buffer prevents the solution from becoming too acidic. 

Acid-catalyzed hydrolysis of isobutylene oxide (8) is >750 times faster than that of ethylene oxide (6), and > 99% of the glycol product is from addition of solvent at the tertiary carbon.23 These results are consistent with a mechanism in which there is significant positive charge on the tertiary carbon at the transition state, as discussed in the previous section. Butadiene monoepoxide (10) is slightly less reactive than isobutylene oxide,36 and its acid-catalyzed hydrolysis can potentially proceed via a resonance-stabilized allyl cation (Scheme 6). However, the acid-catalyzed hydrolysis of 10 yields 96% of 3-buten-l,2-diol (15) and only 4% of 2-butene-1,4-diol (16),36 and the acid-catalyzed methanolysis of 10 is reported to yield only 2-methoxy-3-buten-l-ol.37 An A-2 mechanism proceeding via transition state 17 may account for the observation that 1,2-diol 15 is the predominant product from acid-catalyzed hydrolysis of 10. The minor yield of the 1,4-diol 16 may be formed from reaction of... 

Moreover, Pd(0)-catalyzed allylations of imidazole with cyclopentadiene monoepoxide... 

There are many compounds closely related to natural products that are associated with novel syntheses. Dehydrated linalool oxide 891, for example, is conveniently made by chlorination of linalool acetate (28 acetate) with calcium hypochlorite, then cyclization of the allyl chloride 892 with sodium hydroxide and Aliquat 336 in methanol. Once obtained 891 was converted to the dehydrogenated lilac alcohols 893 (R = H). The monoepoxides (on the isopropenyl group) were transformed in a mixture of diacetates that were pyrolyzed to the acetates 893 (R = Ac). Linalool oxide epoxides (894) have... 

The Simmons-Smith cyclopropanation reaction Stereochemically controlled epoxidations Regio- and Stereocontrolled Reactions with Nucleophiles Claisen-Cope rearrangements Stereochemistry in the Claisen-Cope rearrangement The Claisen-Ireland rearrangement Pd-catalysed reactions of allylic alcohols Pd-allyl acetate complexes Stereochemistry of Pd-allyl cation complexes Pd and monoepoxides of dienes The control of remote chirality Recent developments Summary... 

A clever variation on the reactions of allylic acetates is the palladium-catalysed reaction of monoepoxides of dienes with nucleophiles. These monoepoxides can be made in two chief ways. If the diene is symmetrical 264, epoxidation of one of the alkenes occurs more rapidly than the epoxidation of the monoepoxide because the HOMO ( /2) of the diene is higher in energy and therefore more nucleophilic than the HOMO (ji) of an alkene. It is simply necessary to buffer the epoxidation reagent as these monoepoxides 265 are sensitive to acid (chapter 17). 

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. 

Stereoselective transannular cyclizations to hydroazulene systems are also described. These reactions are initiated by ionization of cyclodecenol to form an allylic cation or by oxirane ring opening in cyclodecadiene monoepoxides. 

Olefin epoxidation is not only important in the manufacture of bulk chemicals, e. g. ethylene and propylene oxides, but is also a widely used transformation in the fine-chemicals industry [1], Ethylene oxide is manufactured by vapor-phase oxidation of ethylene, with air or oxygen, over a supported silver catalyst [2], This method is not generally applicable as olefins containing allylic or other reactive C-H bonds give complex mixtures of products with low epoxide selectivity. The method has recently been extended to some other olefins that do not contain reactive allylic C-H bonds, e. g. butadiene, styrene, norbornene, and tert-butyl ethylene [3]. Some of these products, e. g. butadiene monoepoxide and styrene oxide, have potential applications as fine chemicals/intermediates. 

Bis[dicarbonylchlororhodium(I)] and bis[(l,5-cyclooctadiene)chlororhodium(I)], Epoxide opening. The monoepoxide of a diene is regioselectively attacked by nucleophile (ArNHR, ROH) at the allylic position using [Rh(CO)2Cl]2 as catalyst, affording anil-1,2-amino alcohols and alkoxy alcohols. The results are apparently complementary to those obtained from the Pd-catalyzed process. 

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