This work begins with a review of practical cycloaromatization methodologies utilizing 1,3-dien-5-yne subunits. As a valuable addition to this body of literature, an ambient temperature dienyne cycloaromatization pathway resulting from the formal CH activation of an allylic methyl group and subsequent alkyne 1,2-insertion triggered by cationic cyclopentadienyl ruthenium complexes (CpRu) has been discovered. This cyclization route is fundamentally different to previous studies with CpRu that resulted in the formal Hopf product and the new reactivity appears to be correlated with the bulk of the alkyne substituent. Mild levels of catalysis and selectivity have been observed for cis-1-allylic substituted dienynes, although trans-allylic dienynes were also found to be viable substrates for the stoichiometric reaction. Three transient ruthenium-dienyne complexes have been identified from the reaction of a TMS substituted dienyne, one of which is derived from the trans-1-allylic dienyne and the other two appear to be in equilibrium by ligand exchange as supported by VT NMR studies. Kinetic investigations have ruled out metal [eta]²-alkyne coordination as the reaction-triggering event as previously proposed in similar transformations. Two reaction pathways currently being considered are a [1,7]-hydrogen shift mechanism and a metal C-H insertion mechanism. In continuation of previously described metal-triggered cycloaromatizations of dienynes and enediynes, we have investigated in situ stereoselective [eta]⁶-complexation of the products from these reactions by use of chiral substrates. Use of allylic or propargylic stereocenters led to diastereomeric ratios (d.r.) as high as 8:2. The highest stereoselectivities were found by use of a Cp* versus a Cp ligand and the relative stereochemistry for the major and minor products for both reactions were found to be consistent by X-ray structure characterization. Arene binding experiments have ruled out a mechanism in which the selective binding step occurs by complexation of the free arene. Finally we have uncovered a mode of cycloaromatization for enediynes unrelated to the Bergman mode. The reaction occurs predominately in CDCl3 and is promoted by 1,4-cyclohexadiene and HCl. Intermediacy of a cis,cisyne is suspected and the current mechanistic hypothesis involves a cascade of pericyclic reactions leading to product initiated by a [1,7]-hydrogen shift from the dienyne

Background

Our study was performed to evaluate the image quality of 3 T MR wrist arthrograms with attention to ulnar wrist structures, comparing image quality of isotropic 3D proton density fat suppressed turbo spin echo (PDFS TSE) sequence versus standard 2D 3 T sequences as well as comparison with 1.5 T MR arthrograms.

Methods

Eleven consecutive 3 T MR wrist arthrograms were performed and the following sequences evaluated: 3D isotropic PDFS, repetition time/echo time (TR/TE) 1400/28.3 ms, voxel size 0.35x0.35x0.35 mm, acquisition time 5 min; 2D coronal sequences with slice thickness 2 mm: T1 fat suppressed turbo spin echo (T1FS TSE) (TR/TE 600/20 ms); proton density (PD) TSE (TR/TE 3499/27 ms). A 1.5 T group of 18 studies with standard sequences were evaluated for comparison. All MR imaging followed fluoroscopically guided intra-articular injection of dilute gadolinium contrast. Qualitative assessment related to delineation of anatomic structures between 1.5 T and 3 T MR arthrograms was carried out using Mann-Whitney test and the differences in delineation of anatomic structures among each sequence in 3 T group were analyzed with Wilcoxon signed-rank test. Quantitative assessment of mean relative signal intensity (SI) and relative contrast measurements was performed using Wilcoxon signed-rank test.

Results

Mean qualitative scores for 3 T sequences were significantly higher than 1.5 T (p < 0.01), with isotropic 3D PDFS sequence having highest mean qualitative scores (p < 0.05). Quantitative analysis demonstrated no significant difference in relative signal intensity among the 3 T sequences. Significant differences were found in relative contrast between fluid-bone and fluid-fat comparing 3D and 2D PDFS (p < 0.01).

Conclusions

3D isotropic PDFS sequence showed promise in both qualitative and quantitative assessment, suggesting this may be useful for MR wrist arthrograms at 3 T. Primary reasons for diagnostic potential include the ability to make reformations in any obliquity to follow the components of ulnar side wrist structures including triangular fibrocartilage complex. Additionally, isotropic imaging provides thinner slice thickness with less partial volume averaging allowing for identification of subtle injuries.