X-Ray crystallographic and 13C nuclear magnetic resonance studies of 3,4,5,6-tetrahydro-2H-1,3,4-oxadiazin-2-ones derived from ephedrine and pseudoephedrine

Self-association and stereochemistry study of (5R)-4-methyl-5-phenyl-1,3,4-oxadiazinan-2-one

C10H12N2O2, M r = 191.21, P21, a = 5.5771(7), b = 27.841(3), c = 6.906(1) Å, β = 111.937(9)°, Z = 4, R 1 = 0.0462. The two independent molecules in the asymmetric unit are linked through two very strong quasi centro-symmetric hydrogen bonds. The oxadiazinone rings, of both molecules, show the pyramidal inversion at N-4 nitrogen, thus resulting in a C(R)N(S)—C(R)N(R) diastereomeric pair. The analysis of the IR N-H stretching band (in the solid and in carbon tetrachloride solution) and the 13C NMR experiment at low temperature are in agreement with the X-ray crystal structure.

(5R,6S)-4-Isopropyl-5-methyl-6-phenyl-3-propanoyl-2H-1,3,4-oxadiazinan-2-one

The title compound, C₁₆H₂₂N₂O₃, was synthesized during the course of a study on (1R,2S)-norephedrine-derived 1,3,4-oxadiazinan-2-ones. The conformation adopted by the isopropyl group is pseudo-axial relative to the oxadiazinan core. The allylic strain contributes to this conformational arrangement.

(5S,6R)-5-Methyl-6-phenyl-4-propyl-1,3,4-oxadiazinane-2-thione

The title molecule, C13H18N2OS, is an oxadiazinanthione derived from (1R,2S)-norephedrine. There are two molecules in the asymmetric. Both adopt roughly half-chair conformations; however, the 5-position carbon orients out of opposite faces of the oxadiazinanthiones plane in the two molecules. In the crystal structure, they are oriented as a dimer linked by a pair of N—H...S hydrogen bonds. The absolute configuration has been established from anomalous dispersion and confirms the known stereochemistry based on the synthetic procedure.

(5S,6S)-4,5-Dimethyl-3-methyl-acryloyl-6-phenyl-1,3,4-oxadiazinan-2-one

The title compound, C₁₅H₁₈N₂O₃, is an example of an oxadiazinan-2-one with significant inter­action between the N₃-acyl and N₄-methyl groups. These steric inter­actions result in a large torsion angle between the two carbonyl groups, not present with acyl substituents with less steric demand.

(4R,5S)-5-Benzyl-4-isopropyl-1,3,4-oxadiazinan-2-one

The title compound, C(13)H(18)N(2)O(2), is an N(4)-isopropyl-l-phenyl-alanine-based oxadiazinanone. Although the two mol-ecules in the asymmetric unit are oriented appropriately for hydrogen bonding, the distance between the donor and acceptor atoms is large enough to support only weak, if any, hydrogen bonding. The absolute configuration is known based on the known starting compounds in the synthetic procedure.

Nickel-Catalyzed Addition of Dimethylzinc to Aldehydes across Alkynes and 1,3-Butadiene: An Efficient Four-Component Connection Reaction

In the presence of 10 mol % of Ni(acac)(2), four components comprising Me(2)Zn, alkynes, 1,3-butadiene, and carbonyl compounds combine in this order in 1:1:1:1 ratio to furnish (3E,6Z)-octadien-1-ols 1 in good yields. Similarly, the coupling reaction of Me(2)Zn, 1,omega-dienynes 5, and carbonyls furnishes 1-alkylidene-2-(4'-hydroxy-(1'E)-alkenyl)cyclopentanes and -cyclohexanes 6 and their oxygen and nitrogen heterocycle derivatives in good yield and an excellent level of 1,5-diastereoselectivity with respect to the cycloalkane methine carbon and the OH-bearing carbon of the C2 side chain. The reaction is completed in most cases within 1 h at room temperature under nitrogen, tolerates an ester, a hydroxy, an allyl and propargyl ethers, an allylamino, and a pyridyl functionalities, and accommodates a variety of aromatic and aliphatic alkynes and carbonyls (aldehydes and ketones).

Intramolecular Chiral Relay at Stereogenic Nitrogen. Synthesis and Application of a New Chiral Auxiliary Derived from (1R,2S)-Norephedrine and Acetone

(1R,2S)-Norephedrine has been employed in the synthesis of a novel 3,4,5,6-tetrahydro-2H-1,3,4-oxadiazin-2-one via reductive alkylation with acetone, N-nitrosation, reduction, and cyclization. The oxadiazinone was treated with either propionyl chloride or 3-thiophenylpropionyl chloride to afford the corresponding N(3)-acylated oxadiazinones 9a and 9b, respectively. X-ray crystallographic analysis of the N(3)-thiophenylpropionyl oxadiazinone 9b revealed that the C(2)-urethane carbonyl and the N(3)-carbonyl are arranged in an anti-periplanar conformation. The oxadiazinones were subsequently applied in the titanium-mediated asymmetric aldol addition reaction by treatment with titanium tetrachloride, triethylamine, and a variety of aldehydes at 0 degrees C. The aldol adducts 10a-i and 11a,b were found to have diastereoselectivities ranging from 8:1 to >99:1 favoring the formation of the non-Evans syn configuration. The absolute stereochemistry of the adduct 10a was determined by acid hydrolysis. This process afforded the N(4)-isopropyloxadiazinone 8 and (2S,3S)-3-hydroxy-2-methyl-3-phenylpropanoic acid 14 in >/=95% enantiomeric excess.

Toward the Development of a Structurally Novel Class of Chiral Auxiliaries. Conformational Properties of the Aldol Adducts of Oxadiazinones: Observation of Unusual Shielding Effects

Asymmetric aldol reactions were conducted with the titanium enolate of N(3)-hydrocinnamoyl-3,4,5,6-tetrahydro-2H-1,3,4-oxadiazin-2-one to afford aldol adducts 5a-j. The dominant product of the asymmetric aldol reaction was the non-Evans syn adduct as determined by (1)H NMR spectroscopy and X-ray crystallography. When evaluating the (1)H NMR spectra of adducts 5a-j, a highly shielded signal with an average chemical shift of 0.05 ppm was observed. This signal was readily determined to be the C(5)-methyl group of the oxadiazinone. It is presumed that the overall conformation adopted by the aldol adducts in solution places an aromatic ring of the N(3)-substituent in close proximity to the C(5)-methyl group. An investigation of this conformational preference is conducted employing (1)H NMR spectroscopy, X-ray crystallography, and computational methods.

Conformational studies of N(3)-substituted [1,3,4]-oxadiazinan-2-ones

Pseudoephedrine-based [1,3,4]-oxadiazinan-2-ones acylated at the N(3)-position with either acetyl (2a), propionyl (2b), or phenylacetyl (2c) substituents are known to undergo conformational changes that are observable by (13)C NMR spectroscopy. The conformational properties of new [1,3,4]-oxadiazinan-2-one derivatives 2d-k are examined by X-ray crystallography and variable-temperature (13)C NMR spectroscopy and further evaluated by semiempirical AM1 calculations. The collected data reveal that the conformational changes of the overall ring system are dependent upon the stereoelectronic factors of the N(3)-substituent.

Toward the development of a structurally novel class of chiral auxiliaries: diastereoselective aldol reactions of a (1R,2S)-ephedrine-based 3,4,5,6-tetrahydro-2H-1,3,4-oxadiazin-2-one

[reaction: see text] Asymmetric aldol addition reactions have been conducted with (1R,2S)-ephedrine-derived 3,4,5,6-tetrahydro-2H-1,3,4-oxadiazin-2-one (2). Diastereoselectivities range from 75:25 to 99:1 for the formation of the crude non-Evans syn adducts 8a-h. The facial selectivity of the enolate is directed by the stereogenic N(4)-methyl substituent. Aldol adduct 8a is readily cleaved by acid hydrolysis to afford (2S,3S)-3-hydroxy-2-methyl-3-phenylpropionic acid (9) in >95% ee.