Browsing by Author "Balanay, Mannix P."
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- 1,6-Conjugate Additions of Carbon Nucleophiles to 2-[(1E,3E)-4-Arylbuta-1,3-dien-1-yl]-4H-chromen-4-onesPublication . Albuquerque, Hélio; Santos, Clementina M.M.; Balanay, Mannix P.; Cavaleiro, José; Silva, ArturKGaA, Weinheim The 1,6-conjugate addition of nitromethane to 2-[(1E,3E)-4-arylbuta-1,3-dien-1-yl]-4H-chromen-4-ones was accomplished and led mainly to the corresponding β-(nitromethyl)chromones. (E)-5′-(Nitromethyl)-3′-styryl-[1,1′-biphenyl] -2-ol and 3′-aryl-2′-nitro-5′-(nitromethyl)spiro[chromane-2,1′-cyclohexan]-4-one derivatives were also isolated as minor products from tandem processes, which result from the addition of a second molecule of nitromethane. The nucleophile scope was investigated with malononitrile, acetylacetone, ethyl cyanoacetate, and diethyl malonate, which gave the expected 1,6-addition products; in the last case, it was also possible to isolate a minor product formed through a 1,8-/1,6-addition sequence. Computational calculations provided a rationale for the experimental reactivity of carbon nucleophiles with 2-[(1E,3E)-4-arylbuta-1,3-dien-1-yl] -4H-chromen-4-ones. The further functionalization of some adducts allowed the preparation of new nitrogen-containing heterocyclic compounds, such as new styrylpyrrolidines and new pyrazole and bis(pyrazole) derivatives.
- Conjugate additions of carbon nucleophiles to chromones substituted with extended π-systems at C-2Publication . Albuquerque, Hélio; Santos, Clementina M.M.; Balanay, Mannix P.; Cavaleiro, José; Silva, ArturThe conjugate addition of carbon nucleophiles to electron deficient alkenes is an important method for carbon-carbon bond formation [1]. Generally, 1,4-conjugate addition reactions are more developed than its analogous 1,6- or 1,8-additions, mainly due to the presence of several electrophilic sites in extended conjugated systems as well as the inherent difficulties in controlling the regioselectivity (1,4- vs. 1,6- vs. 1,8-addition) [1]. In this work, we provide new experimental and computational insights about the reactivity of the 3,2:α,β:γ,δ-triunsaturated system of the 2-[(1E,3E)-4-arylbuta-1,3-dien-1-yl]-4H-chromen-4-ones 1 in conjugate addition reactions with carbon nucleophiles (Figure 1). The 1,6-conjugate addition of nitromethane to chromones 1 afforded the corresponding β-(nitromethyl)chromones 2 as major products. (E)-5′-(Nitromethyl)-3′-styryl-[1,1′-biphenyl]-2-ols 3 and 3′-aryl-2′-nitro-5′- (nitromethyl)spiro[chromane-2,1′-cyclohexan]-4-ones 4 were also isolated as minor products, which result from tandem reactions [2]. The nucleophile scope (malononitrile, acetylacetone, diethyl malonate and ethyl cyanoacetate) of this reaction was also assessed and gave, in all cases, the expected 1,6-addition products 5 as major products. Computational calculations showed that the reaction is probably kinetically driven towards 1,6-addition. The further functionalization of some adducts allowed the preparation of new nitrogen-containing heterocyclic compounds, such as pyrazole derivative 6 and styrylpyrrolidines 7 [2].