Abstract
The title compound, C20H23FN2O4, is the product of a ring-expansion reaction from a seven-membered fluorinated hexa-hydro-azepine to a nine-membered azonine. The nine-membered azonine ring of the mol-ecule adopts a chair-boat conformation. The C=C and C-N bond lengths [1.366 (3) and 1.407 (3) Å, respectively] indicate the presence of conjugation within the enamine CH2-C=C-N-CH2 fragment. The substituent planes at the C=C double bond of this fragment are twisted by 16.0 (3)° as a result of steric effects. The amine N(Et) N atom has a trigonal-pyramidal configuration (sum of the bond angles = 346.3°). The inter-planar angle between the two carboxyl-ate substituents is 60.39 (8)°. In the crystal, mol-ecules form zigzag chains along [010] by inter-molecular N-H⋯O hydrogen-bonding inter-actions, which are further packed in stacks toward [100]. The title azonino-indole might be considered as a candidate for the design of new Alzheimer drugs.
Highlights
The reaction mixture was stirred for 2 h at room temperature with
Compound I is isostructural to the non-fluorinated analog published by us very recently (Nguyen et al, 2017)
The solvent was removed in vacuo and the residue was chromatographed over silica with ethylacetate:hexane as eluent to yield the target fluorinated azoninoindole I (22%) and 3-methoxymethylindole II
Summary
Eight-, nine-, and ten-membered heterocycles, often referred to as medium-sized rings, remain largely unexplored because of the lack of general convenient routes for their synthesis Such medium-sized heterocycles, in particular azonine, frequently occur in natural products, such as alkaloids (Neuss et al, 1959, 1962; Uprety & Bhakuni, 1975), and they are considered to be promising fragments in drug design. Voskressensky and his group have pioneered the tandem transformation of fused tetrahydropyridines into azines bearing an enamine moiety in the eight-membered ring under the action of activated alkynes. The reaction mixture was stirred for 2 h at room temperature with
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