B. E. Davis

Structure of aqua-hexakis(μ2-benzoato)-bis(methanol)-μ3-oxo-triiron(III) benzoate ethanol methanol solvate

[Fe3(O)(C7H5O2)6(CH3OH)2(H2O)]-[C7H5O2]-C2H5OH-CH3OH (1/1/1), Mr = 1191.56, triclinic, P1-, a = 11.591 (3), b = 13.308 (2), c = 20.154 (3) A, alpha = 96.910 (12), beta = 96.95 (2), gamma = 114.10 (2) degrees, V = 2767.1 (9) A3, Z = 2, Dx = 1.43 g cm-3, mu = 8.471 cm-1, Mo K alpha radiation, lambda = 0.7107 A, F(000) = 1234, T = 198 K, R = 0.0522 for 6252 reflections [Fo greater than or equal to 4 sigma (Fo)]. The complex has nearly D3h symmetry with two coordinated CH3OH molecules and one coordinated H2O molecule. The coordination around the Fe atoms is essentially octahedral. Each Fe atom lies slightly out of the plane of the O atoms of the bridging benzoates and is directed towards the mu 3-O atom. The average Fe--O distances are 1.907 (2) A for the mu 3-O atom and 2.010 (1) A for the benzoate O atoms.

4,7-Dimethoxybenzo[c]furan.

The title compound, C10H10O3, is nearly planar with a maximum deviation from planarity of 0.140 (2) A for methoxy atom C11. The geometry of the benzo[c]furan moiety is indicative of a non-aromatic ring system. The bond lengths more closely resemble those of two non-interacting diene systems than those of an aromatic one. There are alternating long and short bond lengths around the ring skeleton with the long and short C-C bonds averaging 1.437 (2) and 1.354 (2) A, respectively. There are close C-H ... O intermolecular contacts which may help stabilize the molecule in the solid state.

A novel dioxabicyclo[3.3.1]nonane, a key intermediate in the synthesis of erythronolide B seco‐acid

In the title compound, (1R,4S,5R,6R,8R)-1-ethyl-4,6,8-trimethyl-2,9-dioxabicyclo[3.3.1]++ +nonan-6-yl 1-imidazolecarboxylate, C16H24N2O4, the 2,9-dioxabicyclo[3.3.1]nonane ring system assumes a double-chair conformation. Bond angles around the ring are enlarged compared to normal tetrahedral values to alleviate some of the overcrowding which results from close intramolecular H...H and C...C contacts. The N-imidazolylcarbonyloxy group is nearly planar with dihedral angles of 5.2 (2) and 6.0 (2) degrees between the imidazole and carbonyl groups for molecules 1 and 2, respectively.

Structure of a tricyclic subunit of manzamine A

(4a alpha,7a beta,10a beta)-2-Benzyl-1,2,3,4,4a,7,7a,8,9,10-decahydro-8,8- dimethylpyrrolo[2,3-i]isoquinolinium iodide, C20H29N2+.I-, M(r) = 424.37, monoclinic, P2(1)/n, a = 9.441 (4), b = 10.378 (4), c = 20.023 (9) A, beta = 91.56 (3) degrees, V = 1961 (1) A3, Z = 4, Dx = 1.44 g cm-3 (188 K), lambda(Mo K alpha) = 0.7107 A, mu = 16.16 cm-1, F(000) = 864, T = 188 K, R = 0.0288 for 3070 reflections [Fo greater than or equal to 4 sigma(Fo)]. The crystal structure determination was undertaken in order to establish the configuration around C10a. The rings of the isoquinoline group are trans, with the pyrrole moiety cis fused. The A ring is in the chair conformation, while the cyclohexene ring, B, is in the boat conformation owing to the cis fusion of the five-membered pyrrole ring. The pyrrole ring, C, assumes the half-chair conformation. The C-N bonds of the quaternary N atom, N8, are longer than those of the tertiary N atom, N2 [1.517 (2) for N8 and 1.463 (2) A for N2].

Structure of a fully protected seco-erythronolide B acid derivative.

(3S,4R,5S,6R,7R,9R,10S,11S,12S,13S,- 14R)-14-Benzyloxymethoxy-10,12-O-carbonyl-4-N- imidazolylcarbonyl-6,7-O-isopropylidene-3,5,7,9,11,- 13-hexamethylhexadec-1-ene-4,6,7,10,12,14-hexol, C38H56N2O9, Mr = 684.87, monoclinic, P2(1), a = 8.7302 (12), b = 15.597 (2), c = 14.463 (2) A, beta = 104.797 (10) degrees, V = 1904.1 (4) A3, Z = 2, Dx (198 K) = 1.19 g cm-3, mu = 0.7893 cm-1, Mo K alpha radiation, lambda = 0.7107 A, F(000) = 740, T = 198 K, R = 0.0301 for 3141 reflections [Fo greater than or equal to 4 sigma (Fo)]. The crystal structure was undertaken to determine the stereochemistry of the title compound. The molecule is folded on itself in such a way that the portion of the molecule from the phenyl ring at C44 and extending to C28 forms nearly a single turn of a right-handed screw. Large deviations from ideality for several Csp3-Csp3 bond angles are observed that are presumably due to intramolecular steric effects. The largest deviations are: C3-C4-C5 117.8 (2), C5-C6-C7 121.2 (2), C7-C8-C9 115.3 (2), C9-C10-C11 116.2 (2), C11-C12-C13 117.2 (2), C14-C15-C16 115.5 (3) degrees.

Structure of (±)-(1R*,6S*)-1-benzyloxy-8,11,11-trimethyl-6-phenylthiobicyclo[5.3.1]undec-7-en-3-one

C27H32O2S, Mr = 420.61, monoclinic, P2(1)/c, a = 8.4756(13), b = 14.710(2), c = 18.425(3) A, beta = 99.575(13) degrees, V = 2265.2(6) A3, Z = 4, Dx = 1.23 g cm-3, mu = 1.5567 cm-1, Mo K alpha, lambda = 0.7107 A, F(000) = 904, T = 298 K, R = 0.0630 for 2942 reflections [Fo greater than or equal to 6 sigma (Fo)]. The cyclooctane portion of the [5.3.1] ring system assumes the boat-chair conformation while the cyclohexene portion has the boat conformation. As has been observed in other [5.3.1]undecene systems, ring strain appears to cause a distortion of the geometry of the bridgehead alkene. The bond length C7--C8 [1.343(5) A] is long for an isolated C--C double bond. The Csp2--Csp3 bond lengths at C7 are asymmetric with C7--C6 being 1.498(5) A while C7--C11 is 1.535(5) A. The maximum deviation from ideality for the torsion angles around the double bond is 16.2(4) degrees (absolute value). This twist in the alkene group is reflected in the non-planarity of the group [max. deviation 0.193(6) A for C9] and in the dihedral angle between the nearly planar portions (C6, C7, C8, C11 and C7, C8, C9, C15), which is 9.4(2) degrees.

Novel 2- and 5-Azido-N-(diphenylcarbamoyl)proline Methyl Esters. Examples of a Novel Proline Oxidation

The crystal structures of two azido-substituted proline derivatives are reported. Racemic 2-azido-1-(diphenyl-carbamoyl)proline methyl ester, (I), C19H19N5O3, is resolved upon crystallization from methylene chloride-diethyl ether. The azido moieties are nonlinear with N--N--N angles of 173 (1) and 170.3 (2) degrees for (I) and (II) [cis-5-azido-N-(diphenylcarbamoyl)proline methyl ester, C19H19N5O3], respectively. Close intramolecular contacts between the carbonyl O atom of the amide and the central N atom of the azido group are found. The contact distances between N7 and O14 are 2.780 (14) and 2.815 (2) A for (I) and (II), respectively.

Two [7.3.1]Azabicyclo-z-3-ene-1,5-diyne Analogues of Dynemicin A

The crystal structures of methyl 6-methoxy-17-oxo-2-azatricyclo[7.7.1.0(3,8)]heptadeca-3(8),4 ,6,13-tetraene- 11,15-diyne-2-carboxylate ethyl acetate solvate, (1), 2C19H15NO4.0.5C4H8O2, and tricyclo[3.3.1.1(3,7)]decyl 6-methoxy-17-oxo-2-azatricyclo[7.7.1.0(3,8)]heptadeca-3(8),4 ,6,13-tetraene- 11,15-diyne-2-carboxylate ethyl acetate solvate, (2), C28H27NO4.0.5C4H8O2, are reported. For compound (1), two crystallographically independent molecules are observed. Interestingly, for both compounds (1) and (2), a molecule of ethyl acetate is found in the crystal lattice disordered about an inversion center. The azabicyclo[7.3.1]enediyne core appears to be fairly rigid. Only minor differences are observed in the ring conformation between the two independent molecules in (1) and between compounds (1) and (2) themselves. The conformation is also similar to that found in deoxydynemicin A [Shiomi, Iinuma, Naganawa, Hamada, Hattori, Nakamura, Takeuchi & Iitaka (1990). J. Antibiot. 43, 1000-1005] and triacetyldynemicin A [Konishi, Ohkuma, Tsuno, Oki, Van Duyne & Clardy (1990). J. Am. Chem. Soc. 112, 3715-3716]. The transannular diyne distance (C3...C8) averages 3.428 (2) A for compound (1) and is 3.403 (3) A for compound (2).

Novel N-acyl α-azidopyrrolidines (N-acyliminium-ion precursors)

As an alternative to the electrochemical procedure [Shono (1984). Tetrahedron, 40, 811-850], N-acyliminium-ion precursors may be generated utilizing novel hypervalent iodine chemistry. The crystal structures of 2-azido-N,N-diphenylpyrrolidine-1-carboxamide, C 17 H 17 N 5 O, and 2,5-diazido-N-(3,4,5-trimethoxybenzoyl)pyrrolidine, C 14 H 17 N 7 O 4 , are reported. In both instances the pyrrolidine ring is found in the half-chair conformation. The azido groups are non-linear with an average bond angle of 172.9 (1)°

Structure of a chiral intermediate in the synthesis of (+)-19-epiajmalicine.

[2S*-(2 beta,3 alpha,6 alpha,12b beta)]-Methyl 3-acetyl-1,2,3,4,6,7,12,12b-octahydro-6-methoxycarbonyl-indolo+ ++[2,3-a] quinolizine-3-ethanoate, C22H26N2O5, M(r) = 398.46, orthorhombic, P2(1)2(1)2(1), a = 9.463 (2), b = 11.251 (3), c = 18.871 (6) A, V = 2009.2 (9) A3, Z = 4, Dx = 1.32 g cm-3 (178 K), lambda(Mo K alpha) = 0.7107 A, mu = 0.8762 cm-1, F(000) = 848, T = 178 K, R = 0.0536 for 1673 reflections [Fo > or = 6 sigma (Fo)]. Molecules are hydrogen bonded along the 2(1)-screw axis parallel to a. The hydrogen-bond geometric parameters for N12-H12...O19 (related by 0.5 + x, 1.5 - y, 1 - z) are N...O 2.986 (6), H...O 2.30 (5) A, N-H...O 161 (5) degrees. The C and D rings are trans fused with ring-junction torsion angles of -39.6 (5) and 63.8 (5) degrees for C12a-C12b-N5-C6 and C1-C12b-N5-C4, respectively. The conformation of the C ring is half chair with N5 and C6 -0.168 (4) and 0.552 (5) A, respectively, out of the plane defined by the remaining four atoms of the ring. The D ring is in the chair conformation.