Reactions with epoxides vinyl

In contrast to reactions with vinyl epoxides and palladium catalysts, the reactions with rhodium retain the stereochemistry of the alkene fragment during the reaction [20]. This is illustrated by the reactions of trans-37a/h and cis-37a/b, which give only one product possessing the same olefin geometry as the starting epoxides (Eqs. 4 and 5). The retention of olefin stereochemisty has also been documented in allylic functionalizations with iridium catalysts, indicating that similar modes of action may be present [21, 22]. 

By analogy to the DYKAT reactions with vinyl epoxides, Trost et al. have developed the Pd-eatalysed asymmetric dynamic kinetic allylic amination and acyl migration of vinyl aziridines with benzoyl imido carboxylates. As shown in Scheme 2.51, the process afforded the corresponding protected vicinal diamines in high yields and enantioselectivities of up to 93% ee. This methodology was demonstrated to be a platform for the formal synthesis of (-I- )-balanol and analogues. 

Scheme 53 Reaction of organobismuth compounds with vinyl epoxides...

For a review of the reactions of vinylic epoxides with organocopper reagents, see Marshall Chem. Rev. 1989, 89. 1503-1511. 

Cleavage of vinyl epoxides to cis-diols. In the presence of a Pd(0) catalyst, prepared by reaction of BuLi (2 equiv.) with Pd(OAc)2 (1 equiv.) and P(0-/-Pr)3 (excess) in THF, carbon dioxide reacts with vinyl epoxides to give carbonates of vinyl cw-l -diols.1... 

Various unsaturated compounds, such as CO2, isocyanates and aldehydes, undergo Pd-catalysed cycloaddition with vinyl epoxides. Reaction of CO2 with 127 affords cyclic carbonates 128 with retention of the configuration at C(3), offering a method of cis hydroxylation of epoxides [66], and has been used for the synthesis of the side-chain unsaturated (—)-exo-brevicomin (129) [67], The tetrahydrofuran 131 was prepared by [3+2] cycloaddition of activated alkenes such as benzylidene malononitrile (130) with vinyl epoxide via Michael addition and allylation [68],... 

Table VII summarizes additional examples of allylations of 190 and 191 as well as of cytosine 200 and 5-methylcytosine 201 (Scheme 44) with electrophiles 74, rac-166, and rac-204 together with the targeted final products. Reactions with glycoside 74 and with vinyl epoxide 204 always occur with overall retention of configuration. The reactions with cyclopentene derivatives are related to the preparation of synthetic carbanucleosides with antiviral action.

Aryl borates can provide both C-alkylation and O-alkylation products upon reaction with epoxides <07JOC7761>. The reaction shown below exemplifies a general reaction of arylborates with vinyl epoxides <07SL3011>. A number of examples were reported, the yield shown is typical. The ratio of SN2 to SN2 is generally >95 5 and the ratio of C-alkylation O-alkylation is also excellent (usually >95 5). 

The chemistry of this class of complexes is dominated by the 7r-allyliron tricarbonyl lactone complexes (155), which have been studied extensively and reviewed. Compounds (155) are normally prepared by reaction of vinyl epoxides with a source of Fe(CO)4 , such as (1) and photolysis, (2) and heat, or (2) in Tetrahydrofinan (THF) or with ultrasonication (see Sonication) the latter two methods are considered to be superior. It has been reported that butene-1,4-diols, particularly the cis isomers, (with or without Lewis acids), 3-butene-1,2-diol sulfites, 3,6-dihydrooxazmes, or related compounds also give (155) with (2). The complexes are isolated as anti isomers at C-1. Substituents at C-3 are oriented syn when not constrained in a ring, whereas... 

The reaction of 2-pyrimidone with vinyl epoxide 16 also takes place under neutral conditions, as oxidative addition of 16 to palladium(O) generates an alkoxide that is sufficiently basic to deprotonate 2-pyrimidone22. In contrast, allyl ester (lS,4/ )-18 demands the use of the potassium phthalimide salt for C-N bond formation33. Similar to the purine /V-allylations with 16 and 18, only the depicted isomers 26 and (15,4f )-27 result. Potassium phthalimide thus represents another ammonia equivalent in palladium(0)-catalyzed allylic substitutions66. 

The biphasic double carbonylation of phenyloxiranes under PT conditions affords 4,5-dihydro-4-phenylfuran-2,3-diones [162]. A similar reaction involving 2-phenylthiirane gives the ) -mercapto-substituted acid [163]. The PTC reaction of vinyl epoxides with CO and Mel in the presence of catalytic amounts of Co2(CO)h and TDA-1 affords /ff-hydroxy acids [164]. 

Diethylaluminum phenylthiolate (l).1 The reagent is prepared from triethyl-aluminum and thiophenol and is used without isolation. The alumi um reagent reacts regio- and stereoselectively with vinyl epoxides (2) to afford mainly (Z)-4-phenylthio-2-butene-l-ol derivatives (3). In contrast reaction of vinyl epoxides with C6H5SH and N(C2H5)3 gives mainly the (E)-isomer. Lithium benzenethiolate does not cleave vinyl epoxides at 25°. 

In their reaction with bases, epoxides appear to undergo typical S 2 attack. Ammonia,18 amines,19 alkoxides,20 and sodio derivatives21 react at the less substituted carbon atom (except in vinyl systems, see p. 222), and at least in one case which has been studied inversion of configuration results (p. 202). 

Another standard method for the synthesis of 2-oxazolidinones is by reaction of epoxides with isocyanates. Although 4,5-disubstituted derivatives are not readily accessible by this route, it has been shown that iminodioxolanes (192) add to epoxides in the presence of AICI3 to afford these oxazolidinones in high yield <9lJOC2684>. The reaction proceeds through a spirocyclic intermediate (193) (Scheme 96). The reaction of vinyl epoxides with aryl isocyanates is facilitated by palladium catalysis (Equation (28)) <89TL3893>. The products are obtained by a double inversion process, but... 

Although the stereochemical courses of these displacements are basically also mechanism-controlled, the predictions are not as reliable as in the case of the S 2 reactions. However, cuprates have been shown to undergo SN2 -displace-ments with vinyl epoxides [reaction (10) in Scheme 4) [13] and y-mesyloxy-a,P-enoates [reaction (11), Scheme 4) [14] with extremely high stereo control. A Mit-sunobu-type Sn2 -displacement is shown in reaction (12) (Scheme 4) [15]. 

A. M. Castano, M. Mendez, M. Ruano, and A. M. Echavaren, Reaction of vinyl epoxides with palladium-switchable bisnucleophiles Synthesis of carbocycles, J. Org. Chem., 66 (2001) 589-593. 

Reaction with vinyl oxiranes. a, 3-Unsaturated epoxides, for example (1), on irradiation in the presence of iron pentacarbonyl give lactones such as (2). When warmed, (2) loses CO and is converted into the Fe(CO)3 complex of the... 

In the C-0 bond cleavage reaction of vinyl epoxides by a palladium complex, formic acid acts as a good proton and hydride donor evolving CO2 (Eqs. 3.24 and 3.25). Zero-valent palladium complex favors the attack at an allylic carbon in an Sn2 manner to give i/ -allylpalladium(II) complex with inversion of configiuation, and formate anion coordinates to the palladium center (Scheme 3.50). Then, decarboxylation of the formate affords palladium hydride, which attacks the ry -allyl moiety from the endo side. Thus, 1,2-addition of hydrogen atoms takes place regioselectively with inversion at the allylic carbon [94]. 

When such C-0 bond activation reaction of vinyl epoxide is carried out in the presence of CO2 [96] or isocyanates [97], nucleophilic attack of the allyloxoanion at the electron deficient carbons takes place to give carbonates and oxazolidine with retention of configuration (Eqs. 3.26 and 3.27). Palladium... 

The synthesis of benzyl 4-C-acetyl-6-deoxy-2,3-0 nethylene-a-D-gluco-pyranoside (7) and -galactopyranoside (8) have been achieved from the 4-uloside (9) by reaction with vinyl magnesium bromide, followed by epoxidation, reduction, and oxidation to the C-acetyl derivative. The g /wco-isomer is the favoured product in the Grignard reaction, but when 2-lithio-2-methyl-1,3-dithian was reacted with (9), the galacto-isomer was formed exclusively, from which (8) was obtained by reaction with mercuric salts in the usual way. ... 

B.i.a. Reactivity and Regioselectivity. As a model for studies on the Pd-catalyzed addition of carbon nucleophiles on acyclic vinyl epoxides, butadiene monoxide has been studied extensively. Nucleophiles attack predominantly at the less hindered position of the cationic Tr-allylpalladium complex. Due to steric effects and in some part for electronic reasons, it appeared that with vinyl epoxides, highly regioseleclive reactions took place and 1,4-addition of the nucleophile is generally the major process. 

C.ii.a. Silyl Derivatives. A Japanese gronp recently reported an original Pd-catalyzed reaction with vinyl- or aryl-fluoro silyl derivatives and vinyl epoxides. " A mechanism involving a zwitterionic TjLallylpalladinm silicate intermediate has been proposed (Scheme 5). Intramolecular transmetallation can give two 17 -allylorganopalladium complexes in equilibrium. The steric bulkiness of the phosphine ligand as well as its electronic affinity are responsible for the 1,2/1,4-product distribution. 

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