Sheldon E. Cremer

The interaction of fluoride ion with organosilicons: facile isomerizations and new reactions of silicon hydrides

Abstract Cesium fluoride isomerization of several derivatives of 3-silabicyclo[3.2.1]octane and 2-silabicyclo[2.2.1]heptane as well as chiral α-NpPhMeSiH are described. The effect of solvent, 18-crown-6 ether, and other salts is discussed. Associated side reactions prompted study of the conversion of Ph3SiH to Ph3SiF by CsF and the identification of the products formed from the reaction of Ph3SiH with DMF, N-methylformanilide, and benzamide in the presence of metal fluorides.

Synthesis, Characterization, and Reactions of Mono and Bicyclic Phostones

Abstract Improved methods for the synthesis of 5- and 6-membered ring phostones 2 and 1 as well as original preparations of bicyclic phostones 4 (n=1,2) have been successfully executed. The preparation of the 4-membered ring 3 was more elusive, but the observed products indicated its presence as an intermediate which underwent further transformations. Reaction of 1 with 2,2,6,6-tetramethylpiperidide at low temperature, followed by treatment with a variety of alkyl halides gave the expected alkylation products whose cis/trans stereochemistry was dependent on the reaction conditions. Subsequent ring closure of the cis or trans alkylated product 10, gave only the cis fused bicyclic product 4. In fact, other synthetic routes to 4 produced only the cis isomer. The mechanisms and stereochemistry of these various conversions will be discussed.

PREPARATIONS AND TRANSFORMATIONS OF BIFUNCTIONAL EXO-2-PHOSPHORUS SUBSTITUTED BICYCLO[2.2.1]HEPTANES

Abstract The secondary phosphonate ester exo-2-(dimethoxyphosphoryl)bicyclo[2.2.1]heptane 1 was prepared by literature methods on a mole scale. This synthetic method was extended to include the stereoselective preparation of the exo-diethyl phosphonate analog 3 in 71% yield. Derivatization of these exo-phos-phonates 1 and 3 required vigorous conditions, but proceeded in moderate to high yields. The configuration about carbon-2 was retained in all but one case. Isomerization about carbon-2 was observed during the desulfurization of exo-thiophosphonic dichloride 15 with triphenylphosphine at 240°C. A 3:2 ratio of exo- to endo-phosphonous dichlorides 16 resulted. When the reaction was conducted at 100°C, exo-phosphonous dichloride 16 was formed without epimerization at carbon-2 (97% exo isomer). The exo-dichloride 16 isomerized to the endo-isomer upon treatment with triphenylphosphine at 240–260°C. The intermediate phosphaalkene 17 was implicated to precede this isomerization. Moreover, intentional isomeriza...

The interaction of fluoride ion with organosilanes: equilibration of the exo/endo isomers of 3-methyl-3-silabicyclo[3.2.1]octane

The exo/endo isomers of the title compound can be obtained as an equilibrium mixture when treated with cesium fluoride in DMF; the observed equilibrium constant is in agreement with theoretical calculations.

13C nuclear magnetic resonance of organophosphorus compounds. VI. 13C spin-lattice relaxation times in phosphorus heterocycles

Abstract Carbon-13 spin-lattice relaxation times have been determined for a series of substituted 2,2,3,4,4-pentamethylphosphetanes (four-membered phosphorus heterocycles), including phosphetanes, phosphetanium salts and phosphetane oxides. Nonprotonated carbons have T 1 values of the order of 8–18 sec while protonated carbons have values ranging from 0.6 to 4.0 sec. The rigidity and, in most cases, isotropic nature of the phosphetanes has allowed comparison of T 1 s and subsequent determination of relaxation mechanisms and probing of the ease of internal rotation for each of the several methyl groups on the basic ring backbone. Situations are observed where pseudoequatorial methyl carbons on C-2 and C-4 have relaxation times shorter than those of the presumably more hindered pseudoaxial methyls attached to the same C-2 and C-4 carbons. This points out the danger of directly equating short T 1 values with steric crowding.

X-RAY CRYSTAL STRUCTURES OF Cis- AND Trans-3-(DIPHENYLHYDROXYMETHYL)-2-ETHOXY-2-OXO-1,2-OXAPHOSPHORINANES AND AN ASSOCIATED STUDY OF HYDROGEN BONDING

Abstract The molecular structures of both the cis(4a) and trans(4b) isomers of 3-(diphenylhydroxymethyl)-2-ethoxy-2-oxo-1,2-oxaphosphorinane were determined by the single crystal X-ray diffraction method. The cis and trans designation refer to the relative spacial arrangements of the phosphoryl oxygen and the substituent group on the α-carbon. The crystallographic data are for 4a: C19H23O4P, Mr = 346.36 monoclinic, P21/c, a = 13.2774(9) A, b = 8.5543(9) A, c = 16.7289(25) A, β = 111.142(10)°, V = 1772.2(4) A3, Z = 4, Dcalc = 1.298 g cm−3, λ(MoKα) = 0.71069 A, μ = 1.70 cm−1, F(000) = 736, T = 298 K, R = 0.065 for 2099 reflections; and for 4b: C19H23O4P, Mr = 346.36, monoclinic, P21/c, a = 9.5120(15) A, b = 12.317(4) A, c = 15.309(3) A, β = 100.717(15)°, V = 1762.3(7) A3, Z = 4, Dcalc = 1.305 g cm−3, μ(MoKα) = 0.71069 A, μ = 1.60 cm−1, F(000) = 736, T = 298 K, R = 0.041 for 1638 reflections. In both structures the diphenylhydroxymethyl group is in an equatorial position, and the 1,2-oxaphosphorinane ring ad...

Conformational and solid‐state studies of diphenyl 1‐hydroxy‐1‐phenylethylphosphonate

The crystal structure of the title compound, diphenyl 1-hydroxy-1-phenylethylphosphonate (1), was determined by the single-crystal X-ray diffraction method. The crystallographic data for 1 are as follow: C20H19O4P, Mr = 354.34, monoclinic, P21/n, a = 9.787(1) A, b = 20.235(1) A, c = 9.797(1) A, β = 106.18(3)°, V = 1863.3(4) A3, Z = 4, Dcalc = 1.26 g/cm3, λ(Mo-Ka) = 0.71073 A, μ = 1.6 cm−1, F(000) = 744, R = 0.018, and Rw = 0.032 for 2258 observed reflections. The solid-state structure in a dimeric packing mode exhibits intermolecular hydrogen bonding of the type P = O···H–O. Infrared solution studies (CCl4) indicate that upon high dilution (10−4 M) the dimers completely dissociate to give conformers with and without intramolecular hydrogen bonds. Theoretical studies (PM3) were undertaken to determine the energy profile about the P–C torsional angle, which exhibited low energy barriers to rotation with no clear minimum energy conformation.

CRYSTAL AND MOLECULAR STRUCTURE OF 4-TERT-BUTYLPHOSPHORINANE 1-SULFIDE DERIVATIVES

Abstract Three derivatives of the parent 4-tert-butylphosphorinane sulfide were prepared and investigated by single crystal X-ray diffraction: trans-4-tert-butyl-1-phenoxyphosphorinane sulfide (2a) and the cis and trans isomers of 4-tert-butyl-1-phenylphosphorinane sulfide (3b and 3a, respectively). Crystallographic data for 2a: space group P21/n (No. 14) with a = 6.1670(6) A, b = 10.999(1) A, c = 23.275(2) A, β = 94.978(7)°, V = 1572.7(5) A3, and Dcalc = 1.193 g cm−3 for Z = 4, R = 0.040; for 3a: space group C2/c (No. 15) with a = 25.826(3) A, b = 6.427(1) A, c = 20.050(3) A, β = 111.57(1)°, V = 3094(1) A3, and Dcalc = 1.143 g cm−3 for Z = 8, R = 0.043; for 3b: space group P21/c (No. 14) with a = 6.2914(7) A, b = 11.632(1) A, c = 21.088(1) A, β = 96.892(7)°, V = 1532.1(4) A3, and Dcalc = 1.155 g cm−3 for Z = 4, R = 0.048. In every structure the phosphorinane ring adopts a chair conformation with tert-butyl group in an equatorial position. The relative spatial arrangement of the latter and the phenoxy or ...

The molecular structures of 3-silabicyclo(3.2.1)octane and endo-3-methyl-3-silabicyclo(3.2.1)octane as determined by gas phase electron diffraction

The molecular structures of 3-silabicyclo(3.2.1)octane (SB3210) and endo-3-methyl-3-silabicyclo(3.2.1)octane (endo-MSB3210) have been determined by gas phase electron diffraction. The average SiC bond lengths, 1.891(4) A for SB3210 and 1.883(3) A for endo-MSB3210, are comparable with the observed SiC bond lengths in silacyclohexane and silacyclopentane. The average CC bond lengths, 1.552(2) A for SB3210 and 1.548(2) A for endo-MSB3210, also compare favorably with the corresponding distances in silacyclopentane and silacyclohexane. Observed flap angles at the silicon atom are 145(4)° in SB3210 and 160(5)° in endo-MSB3210. Both molecules exhibit considerable flattening at the silicon end of the six-membered ring relative to silacyclohexane which has a flap angle of 139°. The observed structures are compared with the results of molecular mechanics calculations, and with experimental structures for several related compounds.

STEREOSELECTIVE PREPARATION OF THE ENDO-2-PHOSPHORUS SUBSTITUTed BICYCLO[2.2.1]HEPTANE SYSTEM

Abstract The secondary phosphonate ester endo-2-(diethoxyphosphoryl)bicyclo[2.2.1]heptane 6 was prepared in stereoselective fashion for the first time by hydrogenation of 2-(diethoxyphosphoryl)bicyclo[2.2.1]hept-2-ene 1. The precursor vinylphosphonate 1 was prepared by two different routes. Of these, the direct preparation of phosphonate 6 from norbornene in 76% overall yield proved to be the most convenient. Treatment of 6 with PCI5 at 105 °C gave exclusively endo dichloride 7. This same reaction at 120–140 °C gave a 3:1 ratio of endo- to exo-phosphonic dichlorides 7 and 8, respectively. When pure 7 or 8 were exposed to PC15 at 120–140 °C isomerization of each occurred.