Axially chiral N-(o-aryl)-2-thioxo-oxazolidine-4-one and rhodanine derivatives: enantiomeric separation and determination of racemization barriers

Determination of barriers to rotation of axially chiral 5‐methyl‐2‐(o‐aryl)imino‐3‐(o‐aryl)thiazolidine‐4‐ones

“…Thus, the replacement of one of the hydrogen atoms at C-5 by a methyl group slightly decreased the barriers to rotation. In the rhodanine derivatives studied earlier 14 , a change of the hydrogen atoms at C-5 by methyl groups has also been found to decrease the barrier to rotation by 1-3 kJ/mole. This decrease may be the result of a change in the bond lengths and angles of the thiazolidine-4-one with the introduction of methyl groups to C-5 of the ring.…”

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

“…Reaction with NaBH 11 4 The reduction reactions of compounds (6)1-6 were carried out by four molecular equivalents of NaBH 4 in THF. It was observed that the reaction took place regioselectively reducing only the C-4 carbonyl and not the C-2, to yield N-(o-aryl)-4-hydroxy-5,5-dimethyl-2-oxazolidinones with 100% diastereoselectivity (compounds 7-12) ( Fig.…”

“…[1][2][3] The enantiomers of these compounds are known to racemize thermally via rotation around the N sp2 -C aryl bond, 2,3 through a planar transition state (Scheme 1). In fact the activation barriers determined for these 2,3 and structurally similar systems 4 revealed that there is a linear relationship between the van der Waals radius of the ortho halogen substituent and the activation barrier to hindered rotation. The reduction of unsymmetrical anhydrides 5 and cyclic amides with NaBH 4 are known to be regioselective.…”

“…The compounds subjected to reduction reaction by NaBH4 , T 1 and T 2 represent the transition states. N-(o-bromophenyl)-4-hydroxy-5,5-dimethyl-2-oxazolidinone(11).…”

Conformational and Stereodynamic Behavior of Five- to Seven-Membered 1-Aryl-2-iminoazacycloalkanes

“…These compounds can be easily converted into their oxo-analogues by exposure to air (Scheme 1). Examples of dynamic conformational analysis due to a C sp 2 –N stereogenic axis have been reported: 4 barbiturates are the most studied class of biologically active compounds, 5 and lactams, 6 pyrroles, 7 indoles, 8 imides, 9 azalidine-4-ones, 10 thiazolidine-2-thiones, 11 and xanthines 12 are found to exhibit stereodynamic properties.…”