Trans-p-nitrostyrenes

Dipolar cycloaddition reactions of thioisoraunchnones (l,3-thiazolium-4-olates) have not been as extensively studied as those of munchnones (l,3-oxazolium-5-olates) despite offering rapid access to novel heterocyclic compounds. The cycloaddition of the thioisomunchnone (52) with trans-P-nitrostyrene results in the formation of two diastereoisomeric 4,5-dihydrothiophenes (53) and (54) via transient cycloadducts. These cycloadducts then undergo rearrangement under the reaction conditions <96JOC3738>. 

Scheme 6.61 Mechanistic proposals of the 12-catalyzed asymmetric Michael addition of diethyl malonate to trans-P-nitrostyrene proposed by the Takemoto group (A, B, and C) and initial enolate complex (D) with the ammonium group as additional hydrogen-bond donor initiating an alternative mechanism suggested by Sods, Ptipai, and coworkers.

Figure 6.26 Multiple hydrogen-bonding tertiary amine-functionalized thioureas screened in the asymmetric Michael reaction between trans-P-nitrostyrene and acetylacetone at 10mol% loading.

The Tsogoeva group, in 2006, reported the introduction of newly designed bifunctional secondary amine-functionalized proline-based thioureas (95 and 96) and the primary amine-functionalized thioureas (97-99) for catalysis of the asymmetric addition of ketones to trans-P-nitrostyrenes (Figure 6.30) [260, 261]. Using... 

Ricci and co-workers introduced a new class of amino- alcohol- based thiourea derivatives, which were easily accessible in a one-step coupling reaction in nearly quanitative yield from the commercially available chiral amino alcohols and 3,5-bis(trifluoromethyl)phenyl isothiocyanate or isocyanate, respectively (Figure 6.45) [307]. The screening of (thio)urea derivatives 137-140 in the enantioselective Friedel-Crafts reaction of indole with trans-P-nitrostyrene at 20 °C in toluene demonstrated (lR,2S)-cis-l-amino-2-indanol-derived thiourea 139 to be the most active catalyst regarding conversion (95% conv./60h) as well as stereoinduction (35% ee), while the canditates 137, 138, and the urea derivative 140 displayed a lower accelerating effect and poorer asymmetric induction (Figure 6.45). The uncatalyzed reference reaction performed under otherwise identical conditions showed 17% conversion in 65 h reaction time. 

Scheme 6.157 Mechanistic proposal for the biflinctional coordination and simultaneous activation of 2,4-pentandione and trans-P-nitrostyrene through thiourea catalyst 148 leading to chiral Michael adducts.

Scheme 5.10 Proline-catalysed Michael additions to trans-p-nitrostyrene.

Carmona, Rodriguez, and co-workers disclosed an unexpeeted catalytic pathway for the AFC reaction between trans-p-nitrostyrenes and iV-methyl-2-methylindole catalyzed by the half-sandwich aqua complex 151. Metal-nitroalkene, metal-ad-nitro, and free-aci-nitro intermediates have been... 

The first organocatalytic conjugate addition of ketones to trani-P-nitrostyrene was independently reported by Barbas [107], and List [108] using L-proline as catalyst with good yields but very low enantioselectivities (0-23% ee). A subsequent study by Enders et al. showed a profound solvent effect in the reaction since in MeOH the enantioselectivity could be increased to 76% for the major syn diastereoisomer in the reaction between 3-pentanone and tran -P-nitrostyrene employing a 20 mol% of... 

Scheme 22.27 Cl L 81-catalyzed Michael addition of aldehydes to substituted trans-P-nitrostyrenes.

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