David M. Aparicio

Diastereospecific Intramolecular Cyclopropanation of Enantiopure 8-Bromo-3-phenylhexahydrooxazolo[3,2-a]pyridin-5-ones

A diastereospecific intramolecular cyclopropanation of (3R,8R,8aS)-8-bromo-3-phenylhexahydrooxazolo[3,2-a]pyridin-5-one 1 and (3R,8S,8aS)-8-bromo-3-phenylhexahydrooxazolo[3,2-a]pyridin-5-one 2 to generate the corresponding enantiopure 3-phenylhexahydro-5H-cyclopropa[3,4]pyrrolo[2,1-b]oxazol-5-ones 3 and 4 in high yield is described. The synthesis of chiral cyclopropanes remains a considerable challenge, especially due to the fact that cyclopropane rings are often found in a variety of natural products and biologically active compounds. Organic chemists have always been fascinated by the cyclopropane subunit which has played and continues to play a prominent role in organic chemistry. Its strained structure, interesting bonding characteristics and value as an internal mechanistic probe have attracted the attention of the physical organic community.1 Simmons-Smith cyclopropanation reaction is one of the most widely used reactions in the organic chemist’s arsenal for the conversion of olefins into cyclopropanes. This popularity is mainly due to the stereospecificity of the reaction with respect to the double bond geometry and its compatibility with a wide range of functional groups. The chemoselectivity of the reaction toward some olefins is excellent and very few side reactions are observed with functionalized substrates.2,3 Many of these reactions proceed in a cheletropic manner and several methods exist for converting alkenes to cyclopropane rings using carbene type reagents. As carbenes themselves are highly reactive it is common for them to be used in a stabilized form, referred to as carbenoid. The metal carbenoid is electrophilic in nature and electron-rich alkenes usually react much faster than electron-poor alkenes. In 152 HETEROCYCLES, Vol. 96, No. 1, 2018

Crystal structure of (2S,4R)-ethyl 4-nitro­methyl-1-[(S)-1-phenyl­eth­yl]-6-sulfanyl­idene­piperidine-2-carboxyl­ate

In the title compound, C17H22N2O4S, a thiopiperidine derivative, the piperidine ring has an envelope conformation with the methylene C atom opposite to the C=S bond as the flap. The nitromethyl substituent is equatorial while the ethoxycarbonyl group is axial. The mean planes of the nitromethyl group, the carboxy group and phenyl ring are inclined to the mean plane through the five planar atoms of the piperidine ring [maximum deviation = 0.070 (4) Å] by 56.8 (2), 83.8 (5) and 87.1 (2)°, respectively. There is an intramolecular C—H⋯O hydrogen bond involving an H atom of the ethoxycarbonyl group and a nitro O atom. In the crystal, molecules are linked by C—H⋯O hydrogen bonds, forming chains along [100]. The chains are linked by further C—H⋯O hydrogen bonds, forming corrugated layers lying parallel to (001).

(1'S,2R,3R)-(-)-2-Hydr-oxy-3-morpholino-3-phenyl-N-(1'-phenyl-ethyl)propion-amide.

In the title compound, C21H26N2O3, the morpholine ring has a chair conformation and the dihedral angle between the two phenyl rings is 59.0 (3)°. The crystal packing is stabilized by intermolecular O—H⋯O hydrogen bonds, generating a ribbon structure along the a axis. An intramolecular N—H⋯O contact is also present.