On the formation of the 1,2-acetonide of (+), (−), and (±) 1,2,4-butanetriol and its corresponding aldehyde

The acetonides $\text{1}$ and $\text{3}$ are components of a 9:1 equilibrium established during their formation.     

Benzyne derived from aryloxazolines. A versatile intermediate.

The benzyne derived from m-chlorophenyl oxazoline adds nucleopiles regiospecifically producing m-substituted products. Electrophiles are also trapped furnishing 1,2,3-trisubstituted benzenes.     

Selective adsorption of 4He on clean LiF (001) surfaces

The selective adsorption of ⁴He on in-situ cleaved LiF surfaces has been studied under improved resolution. The main results are as follows: (1) There are four bound states in the surface potential well, at energies of ?5.8, ?2.2, ?0.6 and ?0.1 meV. The lowest three levels were reported previously. (2) Most of the structure previously designated as “fine structure” is due either to transitions to these four levels via various small reciprocal lattice vectors or to the opening of diffraction channels. (3) The transitions involving the [01] and [01?] reciprocal lattice vectors (i.e., the ones nearly perpendicular to the incident wave vector) are strong; as much as 85% of the specular intensity may be removed. Transitions via the other small reciprocal lattice vectors are much weaker. (4) The widths of the lines are consistent with the velocity distribution, which has a half-width of about 2%. (5) The observed energies agree fairly well with those calculated by Tsuchida for a zeta-function potential, but are not consistent with a Morse potential.     

Anomalous elastic response of silicon to uniaxial shock compression on nanosecond time scales

We have used x-ray diffraction with subnanosecond temporal resolution to measure the lattice parameters of orthogonal planes in shock compressed single crystals of silicon (Si) and copper (Cu). Despite uniaxial compression along the (400) direction of Si reducing the lattice spacing by nearly 11%, no observable changes occur in planes with normals orthogonal to the shock propagation direction. In contrast, shocked Cu shows prompt hydrostaticlike compression. These results are consistent with simple estimates of plastic strain rates based on dislocation velocity data.     

Study of a new rate increasing "base effect" in the palladium-catalyzed amination of aryl iodides

Evidence for an interphase deprotonation of Pd(II)-amine complexes with weak carbonate base has been gained for the first time. When a rate-limiting deprotonation step is involved in the catalytic cycle, controlling the structure (shape and size of the particles) and/or molar excess of the carbonate base used can significantly increase the reaction rate of Buchwald-Hartwig aminations. By taking such a "base effect" into account a general protocol for the intermolecular amination of aryl iodides with all types of amines has been developed based on a standard Pd-BINAP catalyst, using cesium carbonate as the base.     

Unexpected dipivaloyl­ation of 9‐li­thia­ted fluorene: formation of 1‐(fluoren‐9‐yl­idene)‐2,2‐di­methyl­propyl pivalate

Treatment of 9‐li­thia­ted fluorene with pivaloyl chloride provided ap‐9‐pivaloyl­fluorene, (1), the major product, and a minor product ultimately identified as the title compound, C₂₃H₂₆O₂, (2). The latter was also formed directly, but slowly, from 9‐li­thia­ted‐(1) treated with pivaloyl chloride. Although (1) exists exclusively as its less sterically restricted ap rotamer, its sp²‐hybridized anion sterically impedes reaction at the 9‐position from either face. While 9‐li­thia­ted‐(1) is exclusively, but slowly, 9‐methyl­ated with methyl iodide, reaction with pivaloyl chloride, also slow, leads only to the O‐acyl­ated product, (2). The protons of the tert‐butyl‐C=C moiety approach a proton on the fluorene ring to well within the sum of their van der Waals radii, resulting in significant molecular compression, strain and distortion. For example, distortion in the moiety C=C(O)(C) is exhibited by the enlargement of C=C—C angle to 130.6 (2)° at the expense of the corresponding `equivalent' C=C—O angle, which is compressed to 116.46 (19)°.     

sp‐9‐Acetyl­fluorene,the initial acetyl­ation product of 9‐fluorenyl­lithium

The reaction of 9‐fluorenyl­lithium with acetyl chloride (tetra­hydro­furan, 213 K, under argon) provided four products which we have isolated and whose structures we have unequivocally identified for the first time. That of the initially formed component, 9‐acetyl­fluorene (C₁₅H₁₂O), described here, shows it to be exclusively the sp rotamer in its crystalline form. The acetyl C—C=O plane is essentially perpendicular to the planar fluorene ring and there is no indication of rotational restriction. In contrast, related 9‐pivaloyl­fluorene, which we reported previously, is rotationally restricted and exists exclusively as its ap rotamer, in which the pivaloyl C—C=O plane is also almost perpendicular to the fluorene ring.