1‐Methyl‐5‐(trifluoromethyl)azafulvenium Methide, an Intermediate That Undergoes Reaction through “Unusual” cis‐exo‐1,3‐ and trans‐exo‐1,7‐Cycloadditions

Abstract

The generation and reactivity of a new 1‐methyl‐5‐(trifluoromethyl)azafulvenium methide are described. Under microwave‐induced pyrolysis conditions this intermediate could be trapped by dipolarophiles, acting either as a 4π or as an 8π dipole. Quantum chemical calculations carried out at the DFT level of theory allowed the rationalization of the results observed in the cycloaddition of 1‐methyl‐5‐(trifluoromethyl)azafulvenium methide and N‐substituted maleimides. The study revealed that for 1,7‐cycloadducts the major products are obtained in the trans configuration through the unusual exo‐cycloaddition mode, whereas for 1,3‐cycloadducts the cis counterparts are obtained from this unexpected approach. In addition, under flash vacuum pyrolysis or conventional thermolysis conditions 1‐methyl‐5‐(trifluoromethyl)azafulvenium methide undergoes an allowed suprafacial sigmatropic [1,8]H shift leading to the formation of 2‐methyl‐3‐(trifluoromethyl)‐1‐vinyl‐1H‐pyrrole.

Rearomatization of trifluoromethyl sulfonyl dihydropyridines: Thermolysis vs photolysis

“…By unraveling the by-products obtained, regardless of the method used, another interesting outcome is noticed. The formation of 3 isomers of 15 proves that the S-C bond is strong enough to allow the migration of the trifluoromethyl sulfonyl group (-SO 2 CF 3 ) toward the aromatic ring, even though it should suffer its own fragmentation, as confirmed by the detection of HCF 3 and SO 2 through FT-IR measurements. The analysis of all products and reaction conditions resulted in the reaction mechanism proposed for compound 9, which is presented in Scheme 1.…”

“…In addition, we recently reported the thermal behavior of some trifluoromethyl‐1 H ,3 H ‐pyrrolo[1,2‐ c ]thiazole‐2,2‐dioxides (compounds 5 ‐ 8 , Figure ) evaluated by comparing flash vacuum pyrolysis (at 475°C) with the microwave‐induced pyrolysis (MIP at 240°C). In both cases, the azafulvenium methide intermediate was involved and claimed to be responsible for the interesting compounds obtained …”

“…In both cases, the azafulvenium methide intermediate was involved and claimed to be responsible for the interesting compounds obtained. [2,3] This article is published in Journal of Physical Organic Chemistry as a special issue on New Latin American Conference on Physical Organic Chemistry (CLAFQO-14) at Concón, Región de Valparaiso, Chile 2017 by Paulina Pavez G. (Pontificia Universidad Católica de Chile) Currently, we are interested in trifluoromethyl sulfonyl dihydropyridines and their benzene-fused derivatives (compounds 9 and 10, Figure 1).…”

Pericyclic Reactions of Azafulvenium Methides Bearing Internal Dipolarophiles – Synthesis of Chromene and Chromane Derivatives

“…These 1,7‐cycloadducts include chlorin‐ and bacteriochlorin‐type macrocycles (e.g., 8 ), which have relevance in medicinal chemistry 1g. In contrast with this chemical behaviour, 5‐(trifluoromethyl)azafulvenium methides 7 can participate in both 1,7‐ and 1,3‐dipolar cycloadditions 1i–1k. Aza‐ and diazafulvenium methides bearing methyl or benzyl groups at C‐1 or C‐7 undergo sigmatropic [1,8]H shifts to give vinylpyrroles and vinylpyrazoles, respectively.…”

3-Buten-2-one, 4-Ethoxy-1,1,1-trifluoro-

“…The example reported by Peláez and coworkers in 2014 is representative of this class of reactions for aliphatic amines (eq 4) 6. …”