2.3- Butadienoates, cycloaddition with

Methyl 2,3-butadienoate can undergo 1,3-dipolar cycloaddition with nitrones leading to the formation of 528, which would undergo homolytic cleavage of the N-O bond followed by radical rearrangement and coupling to afford benzazepinone 531 [239]. 

Butadienoate esters undergo AICI3 and EtAlCh catalyzed stereospecific [2 + 2] cycloadditions with a wide variety of alkenes to give alkyl cyclobutylideneacetates in good yield. The stereospecificity and ratios of ( )- and (Z)-isomers suggest a [ 2 + v2a] cycloaddition of the ester-Lewis acid complex to the alkene analogous to the cycloaddition of ketenes with alkenes. Similar results are obtained with methyl 2,3-pentadienoate, methyl 4-methyl-2,3-pentadienoate and methyl 2-methyl-2,3-butadi-... 

The phosphane catalyzed [3+2] cycloaddition between aUenoates and activated alkenes have attracted extensive attention since its discovery [95, 96]. Recently, in 2009, Krische and his co-worker reported a phosphane-catalyzed [3+2] cycloaddition of ethyl-2,3-butadienoate 237 with an enone 238 to give the cis-fused cyclopenta[c]pyran 239. They applied this methodology to the total synthesis of the iridoid p-glucoside (+)-geniposide 240, Scheme 3.77 [97], Alternatively, phosphane-catalyzed [3+2] annulation of aUenoates with aldehydes, affording 2-alky-lidenetetrahydrofurans, was reported by He and his co-workers [98]. 

Cycloaddition. In the presence of either C2H5AICI21 or AICI3,2 esters of 2,3-butadienoic acid (1) undergo [2 + 2] cycloadditions at the 3,4-double bond with acyclic or cyclic alkenes to give cyclobutylideneacetic esters. The reaction is considered to involve the vinyl cation H2C— CH - C(OR)OAlCl,. A mixture of... 

Occasionally, molecular mechanics calculations provide a rationale when FMO theory fails to account for a given regiochemical outcome.For example, cycloaddition of C-phenyl-Af-methyl nitrone to methyl 2-methyl-2,3-butadienoate leads exclusively to the S-exo-methylene cycloadduct, as one would expect based upon FMO theory. In contrast, C7-phenyl- -r-butyl nitrone affords only the 4-exomethylene isoxazolidine, a result which clearly cannot be in accord with the same principles (Scheme 12). Molecular mechanics calculations, carried out under the assumption that the relative energy differences between the products parallel the energy differences between transition states, were in accord with the experimental results, suggesting that the difference in behavim- between the two nitrones may have a steric rather than an electronic origin (Table 10). ... 

Nitrone cycloaddition reactions promoted by dichlorotitanium TADDOLate can be improved by using A(-(2-alkenyl)succinimides as the dipolarophiles. Regioselective and enantioselective formation of cyclopentenecarboxylic esters is observed using 8 to catalyze the [3+2]cycloaddition of 2,3-butadienoates with electron-deficient alkenes. ... 

Another example using chiral phosphines as catalysts has been described by Zhang et al. studying the enantioselective [3 + 2] cycloaddition of butadienoates with electron deficient olefins [19]. Thus, the use of catalytic amounts of catalysts 8-10 led to the formation of major adduct 6 in enantiomeric excesses varying from 12 to 93% ee. The best result was observed performing the reaction in toluene at 0 °C in presence of 10 mol% of catalyst 8 (entry 3, Table 2). 

Table 2. Enantioselective cycloaddition of butadienoates with olefins...

The enantioselective Lewis-acid-promoted 2 -t- 2-cycloaddition of trifluoropyruvate with various alkynes produced stable oxetene derivatives for use in the synthesis of pharmaceuticals and agrochemicals. l,4-diazabicyclo[2.2.2]octane (DABCO)-catalysed 2- -2-cycloaddition of allenoates and trifluoromethylketones produced 2-alkyleneoxetanes in good yields and with good diastereo-selectivities dr > 20 1). A cinchona alkaloid (20) catalysed the 2- -2-cycloaddition between tV-sulfonylimines and alkyl 2,3-butadienoates to form / -configured 2,4-disubstituted azetidines in high yields and with high enantioselectivities. ... 

A-Sulfonylaldimines produced by condensation of SES-NFI2 with various aldehydes are converted into enantiomerically enriched aziridines upon reaction with certain sulfur ylides. The same types of aldimines undergo [3 4- 2] cycloaddition reactions with 2,3-butadienoates in the presence of triphenylphosphine to give 2,5-dihydrop3TToles, while that derived from SES-NSO and ethyl glyoxylate reacts efficiently with chiral sulfonimidoyl substituted bis(allyl)titaniumcorr5)lexes to give /3-alkyl-)/,5-unsaturated a-amino acid derivatives. ... 

The reaction of 2,3-butadienoate with SES imines catalyzed by triphenylphosphine provides 2,5-dihydro-p)UTole-3-carboxylates (eq 17) with an excellent yield and a highregioselectivity. Triphenylphosphine reacts with the aUene to form an allyl carbanion, which is trapped by the SES imine in a [3 + 2] cycloaddition. 

Zhu G, Chen Z, Jiang Q, Xia D, Cao P, Zhang X. Asymmetric [3-1-2] cycloaddition of 2,3-butadienoates with electron-deficient olefins catalyzed by novel chiral 2,5-dialkyl-7-phe-nyl-7-phosphabicyclo[2. 2. Ijheptanes. J. Am. Chem. Soc. 1997 119(16) 3836-3837. 

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