Substituent effects in the ring‐chain tautomerism of 4‐alkyl‐2‐aryl substituted oxazolidines and tetrahydro‐1,3‐oxazines

Abstract

The condensation products of 2-aminoethanol or 3-aminopropanol (bearing an alkyl substituent on the carbon adjacent to the nitrogen) with substituted benzaldehydes proved to exist in CDCl 3 at 300 K as threecomponent tautomeric mixtures of the diastereomeric five-or six-membered 1,3-O,N-heterocyclic ring forms and the corresponding imines. For each equilibrium, the electronic effects of the 2-aryl substituents were characterized by the Hammett equation. The steric effects of the alkyl groups could be described by Hansch-type equations for the equilibria involving oxazolidine ring forms. While the alkyl substituents did not cause any significant effect on the ring cis-chain and the ring trans-chain equilibria for tetrahydro-1,3-oxazines, increasing bulk of the 4-alkyl group increased the stability of the cyclic tautomers for the analogous oxazolidines.

Corrigendum: Interfacing Click Chemistry with Automated Oligonucleotide Synthesis for the Preparation of Fluorescent DNA Probes Containing Internal Xanthene and Cyanine Dyes

“…The condensations of differently substituted 2‐aminoethanols with selected aromatic aldehydes in MeOH to afford compounds 1 – 4 were reported earlier, together with their structural assignments and the determination of their ring‐chain equilibria in CDCl 3 8. Condensation of 2‐amino‐2‐phenylethanol with equivalent amounts of seven differently substituted aromatic aldehydes in MeOH led to 2‐aryl‐4‐phenyl‐1,3‐oxazolidines ( 5a – g ) in good yields (Table 1).…”

Five-membered oxaza heterocyclic compounds on the basis of epoxides and aziridines

“…Nucleophilic addition of anion 198 to Schiff base 199 was assumed to be the key step in the [3 + 2]-cycloaddition process (Scheme 112). The use of Schiff bases and epoxides separately in syntheses of heterocycles, in particular heterocyclization of 3-hydroxy-substituted and other Schiff bases, is considered below [228][229][230][231][232][233]. Sharma A complementary ambiphilic pairing strategy was applied to study reactions of epoxy compounds having CH 2 OCH 2 Ph, CH 2 OPh, (CH 2 ) 2 CH=CH 2 , and other groups with arene-and alkenesulfonamides 214 [237] under microwave irradiation.…”

Axially chiral N‐(o‐aryl)‐4‐hydroxy‐2‐oxazolidinone derivatives from diastereoselective reduction of N‐(o‐aryl)‐2,4‐oxazolidinediones: Thermally interconvertible atropisomers via ring‐chain‐ring tautomerization

“…Ring-chain tautomerization has been shown to occur in a number of heterocyclic compounds. 10,[12][13][14][15][16][17][18][19][20] The tautomerism results from an interconversion of the chain and the ring isomers. For compounds 7-12, the two enantiomers (S-M) and (R-P) (see Fig.…”