An Anomeric Effect Drives the Regiospecific Ring‐Opening of 1,3‐Oxazolidines under Acetylating Conditions

Abstract

A series of oxazolidines derived from tris(hydroxymethyl)-aminomethane (TRIS; 1), have been prepared efficiently. Geometries optimized at the B3LYP/6-31G* level of theory, along with the crystal data of compounds 9 and 12 and NOESY correlations, point to a strong endo anomeric effect that anchors a preferential conformation and subsequently dictates the completely regioselective ring-opening of the oxazolidine moiety under acetylating conditions to afford imines instead of N-acetyloxazolidines. This process was moni-

Schiff Bases and Stereocontrolled Formation of Fused 1,3-Oxazolidines from 1-Amino-2-Indanol: A Systematic Study on Structure and Mechanism

“…An interesting signal appears as a singlet at 5.75 ppm, which, together with the absence of any peak attributable to the imine group (HC=N), points to a saturated carbon. In addition, that chemical shift is similar to that of other oxazolidines described previously [ 1 , 2 , 65 , 66 , 67 , 68 , 69 ], which suggests the existence of this heterocycle in 47 . However, it is much more relevant a second singlet at 4.92 ppm, which could be consistent with an oxazine ring.…”

“… where n i and n e are the populations of molecules with imine and enamine structures, respectively ( n i + n e = 1). The same applies to the coupling constant analysis, which can be represented by Equation (2) for the tautomeric equilibrium [ 1 ]. …”

“…It is particularly relevant to the interconversion between acyclic and heterocyclic frameworks with varied stereocontrol. Thus, the condensation of tris(hydroxymethyl) methylamine (TRIS, 1 ) with substituted benzaldehydes gives rise to 1,3-oxazolidines ( 2 ), which afford the corresponding per- O -acetylated imines ( 3 ) upon conventional acetylation conditions ( Scheme 1 ) [ 1 , 2 ]. However, the reaction of TRIS with salicylaldehydes produces Schiff bases ( 4 ), which lead to a mixture of peracetylated imines ( 5 ) and N -acyl-1,3-oxazolidines ( 6 ) after acetylation ( Scheme 1 ).…”

Probing the Reactivity of Cyclic N,O-Acetals versus Cyclic O,O-Acetals with NaBH4 and CH3MgI

“…The reaction is thought to proceed via an iminium ion intermediate formed upon C–O bond rupture, possibly subsequent to chelation with a Lewis acid, if one is present (Figure ). − …”