3β-Acetoxy-12α-chloro-d-friedooleanan-28,14β-olide

The title compound, C32H49ClO4, was obtained along with nitrile and lactam products in the POCl3-catalysed Beckmann rearrangement from 3β-acetoxy-12-hydroxyiminoolean-28-olic acid methyl ester. The mechanism of the transformation leading to the title compound remains unclear and requires further investigation. Rings A, B and E are in chair conformations, ring C has a twisted-boat conformation, ring D a conformation halfway between boat and twisted-boat and rings D and E are cis-fused. In the crystal, molecules are connected by weak intermolecular C—H⋯O hydrogen bonds into layers extending parallel to the bc plane.

The title compound, C 32 H 49 ClO 4 , was obtained along with nitrile and lactam products in the POCl 3 -catalysed Beckmann rearrangement from 3-acetoxy-12-hydroxyiminoolean-28olic acid methyl ester. The mechanism of the transformation leading to the title compound remains unclear and requires further investigation. Rings A, B and E are in chair conformations, ring C has a twisted-boat conformation, ring D a conformation halfway between boat and twisted-boat and rings D and E are cis-fused. In the crystal, molecules are connected by weak intermolecular C-HÁ Á ÁO hydrogen bonds into layers extending parallel to the bc plane.

Comment
In a POCl 3 -catalysed Beckmann rearrangement of 3β-acetoxy-12-hydroxyiminoolean-28-olic acid methyl ester, an unexpected compound with a chlorine instead of nitrogen atom was obtained along with the typical nitrile and lactam products.
The X-ray analysis has revealed that the title compound contains a δ-lactone ring with the C28═O4 group adjacent to C17. Formation of the lactone bridge is possible because of the change in the configuration of the chiral centers C13 and C14. As a result, the ether oxygen atom O3 at C14 and the methyl group at C13 are axial with respect to rings C and D. The former substituent reveals β-configuration, while the latter one has α-configuration. This observation shows that methyl group C27 has undergone 1,2-shift from C14 to C13 retaining its original orientation.
The chlorine atom at C12, belonging to ring C, is oriented equatorially and assumes α-configuration.
In the crystal lattice, the molecules are connected with three-centered weak hydrogen bonds -1+y, 1+z; (ii) x, y, 1+z] into layers extending parallel to the bc plane. The layer thickness is about a half of the a parameter length.

Experimental
The title compound was obtained as a by-product in POCl 3 -catalysed Beckmann rearrangement reaction and recrystallized from ethanol solution at room temperature.
supplementary materials sup-2 Refinement All H-atoms were placed in geometrically calculated positions and were refined with a riding model with C-H = 0.96-0.98 Å and with U iso = 1.2 U eq (C) or 1.5 U eq (C) for methyl groups. The methyl H atoms were refined as rigid groups, which were allowed to rotate. The absolute configuration of the title compound was established by refinement of the Flack (1983) parameter. Fig. 1. The molecular structure of (I), showing the atomic labelling scheme. Non-H atoms are drawn as 30% probability displacement ellipsoids and H atoms are drawn as spheres of an arbitrary size.