Dipolarophiles methyl acrylate

The theoretical interpretation of the results was made (334) in terms of the molecular orbital perturbation theory, in particular, of the FMO theory (CNDO-2 method), using the model of the concerted formation of both new bonds through the cyclic transition state. In this study, the authors provided an explanation for the regioselectivity of the process and obtained a series of comparative reactivities of dipolarophiles (methyl acrylate > styrene), which is in agreement with the experimental data. However, in spite of similar tendencies, the experimental series of comparative reactivities of nitronates (249) toward methyl acrylate (250a) and styrene (250b) are not consistent with the calculated series (see Chart 3.17). This is attributed to the fact that calculation methods are insufficiently correct and the... 

Benzodiazepin-2-ones are converted efficiently into the 3-amino derivatives by reaction with triisopropylbenzenesulfonyl (trisyl) azide followed by reduction <96TL6685>. Imines from these amines undergo thermal or lithium catalysed cycloaddition to dipolarophiles to yield 3-spiro-pyrrolidine derivatives <96T13455>. Thus, treatment of the imine 50 (R = naphthyl) with LiBr/DBU in the presence of methyl acrylate affords 51 in high yield. 

Dipolarophile D6. A complete theoretical study of the 1,3-dipolar cycloaddition reaction of D-glyceraldehyde nitrone (N) to methyl acrylate (MA) has been... 

However, treatment of the precursor 74, where there is no substitution at C(4) (i.e., R = Me) led to a single [3+2] cycloadduct 75 with methyl acrylate. The unstable oxazolines 75, are considered to open spontaneously to their valence bond, 1,3-dipole tautomers 76, which are trapped in situ by the dipolarophile. Use of DMAD led to the formation of the expected 2,5-dihydropyrrole (77), but difficulties in isolation required DDQ aromatization to pyrrole 78 (Scheme 3.19). 

Confirmation was provided by the observation that the species produced by the photolysis of two different carbene sources (88 and 89) in acetonitrile and by photolysis of the azirine 92 all had the same strong absorption band at 390 nm and all reacted with acrylonitrile at the same rate (fc=4.6 x 10 Af s" ). Rate constants were also measured for its reaction with a range of substituted alkenes, methanol and ferf-butanol. Laser flash photolysis work on the photolysis of 9-diazothioxan-threne in acetonitrile also produced a new band attributed the nitrile ylide 87 (47). The first alkyl-substituted example, acetonitrilio methylide (95), was produced in a similar way by the photolysis of diazomethane or diazirine in acetonitrile (20,21). This species showed a strong absorption at 280 nm and was trapped with a variety of electron-deficient olefinic and acetylenic dipolarophiles to give the expected cycloadducts (e.g., 96 and 97) in high yields. When diazomethane was used as the precursor, the reaction was carried out at —40 °C to minimize the rate of its cycloaddition to the dipolarophile. In the reactions with unsymmetrical dipolarophiles such as acrylonitrile, methyl acrylate, or methyl propiolate, the ratio of regioisomers was found to be 1 1. 

When the a-substituent is methyl (R = Me), deprotonation occurs readily with NEt3 at room temperature. Although the cycloaddition step of the resultant ylide with sterically less hindered or reactive dipolarophiles (A-methylmaleimide, methyl acrylate, methyl methacrylate, and dimethyl fumarate) proceeds faster than the ylide generation step, the cycloaddition step becomes rate determining if sterically... 

Similarly, nitrile oxides react with methyl acrylate 2.42 to give the adduct 2.43 with the substituent on C-5 and terminal alkenes also react in this way to place the alkyl group on C-5. Many dipoles react well with electron-rich dipolarophiles, but not with electron-poor dipolarophiles. Other dipoles are the other way round. To make matters even more complex, the presence of substituents on the dipole can change these patterns and impart their own regioselectivity. Thus the carbonyl ylid reaction 2.45 has a well defined regiochemistry determined only by the substituents, since the core dipole is symmetrical. This reaction also illustrates the point that dipolarophiles do not have to be alkenes or alkynes—they can also have heteroatoms. 

Other dipolarophiles (yield, ratio 2-Ph 3-COOMe cis trans) methyl maleate (91%, 5 4) methyl fumarate (83%, 2 3) AMnethyl maleimide (85%, 1 2) methyl acrylate (83%, 5 4). 

Singlet as well as triplet excited states of oxiranes undergo C—C bond scission to produce carbonyl ylides which, upon cydoaddition with dipolarophiles, give tetra-hydrofuran (THF) derivatives. For example, trans- or ds-stilbene oxide on direct photolysis using 254 nm light in the presence of methyl acrylate gave diastereomeric... 

Azine approach. 4,5-Dihydro-6//- 1,2-oxazine 2-oxides undergo 1,3-dipolar cyclo-addition reacting with appropriately substituted alkenes and alkynes to form isoxazolo-[2,3-Z>][l,2]oxazines. With styrene as the dipolarophile in the reaction with the oxazine (87), the product (88) with cis methyl and phenyl groups is formed. With acrylonitrile and methyl acrylate, some trans isomer is formed, but the cis isomer is predominant. The rings are always c/s-fused (77IZV211). 

The benzo derivative (128) reacts as a thiocarbonyl ylide. Addition of N-(p-tolyl)maleimide gives a mixture of the exo (71%) and endo (16%) adducts (129 Ar=p-tolyl), which in hot acetic acid eliminate hydrogen sulfide giving the pyrido[l,2-a]benzimidazole (130 Ar=p-tolyl). Analogous 1 1 cycloadducts (131) are formed with dimethyl maleate, dimethyl fumarate, methyl crotonate and methyl acrylate. In contrast to the transformation (129) —> (130), treatment of the adducts (131 R = H, Me) with hot acetic acid gives the tetracyclic compounds (133) via the benzimidazole derivatives (132 R = H, Me). Reaction with alkynic 1,3-dipolarophiles gives pyrido[l,2-a]benzimidazole (134) by desulfurization of the primary adducts (80CL1369). 

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