Rate of Formation of Industrial Lubricant Additive Precursors from Maleic Anhydride and Polyisobutylene.

The Alder-ene reaction of neat polyisobutylene (PIB) and maleic anhydride (MAA) to produce the industrially important lubricant additive precursor polyisobutylene succinic anhydride (PIBSA) is studied at 150-180 °C. Under anaerobic conditions with [PIB] ∼ 1.24 M (550 g mol-1 grade, >80% exo alkene) and [MAA] ∼ 1.75 M, conversion of exo-PIB and MAA follows second-order near-equal rate laws with k obs up to 5 × 10-5 M-1 s-1 for both components. The exo-alkene-derived primary product PIBSA-I is formed at an equivalent rate. The less reactive olefinic protons of exo-PIB also react with MAA to form isomeric PIBSA-II (k obs up to 6 × 10-5 M-1 s-1). Some exo-PIB is converted to endo-PIB (containing trisubstituted alkene) in a first-order process (k obs ∼ 1 × 10-5 s-1), while PIBSA-I is difunctionalized by MAA to bis-PIBSAs very slowly. The MAA- and PIB-derived activation parameter ΔG ‡(150 °C) 34.3 ± 0.3 kcal mol-1 supports a concerted process, with that of PIBSA-I suggesting a late (product-like) transition state.

Synthesis of key fragments of leiodelide A.

The synthesis of all key fragments of the marine macrolide leiodelide A is described. The polyoxygenated northern subunit is derived from d-xylose, while the southern subunit is rapidly assembled via an aldol reaction and Horner-Wadsworth-Emmons olefination. This highly convergent approach will allow for rapid modification and assembly of several isomers of leiodelide A, which may be necessary considering the assignment of leiodelide B has been previously shown to be incorrect.

Pure flat epithelial atypia (DIN 1a) on core needle biopsy: study of 60 biopsies with follow-up surgical excision.

Flat epithelial atypia (FEA) is recognized as a precursor of breast cancer and its management (surgical excision or intensive follow-up) remains unclear after diagnosis on core needle biopsy (CNB). The aim of this study was to determine the underestimation rate of pure FEA on CNB and clinical, radiological, and pathological factors of underestimation. 4,062 CNBs from 5 breast cancer centers, performed over a 5-year period, were evaluated. A CNB diagnosis of pure FEA was made in 60 cases (1.5%) (the presence of atypical ductal hyperplasia, lobular neoplasia, radial scars, phyllodes tumor, papillary lesions, ductal carcinoma in situ or invasive carcinoma at CNB were exclusion criteria), and subsequent surgical excision was systematically performed. The histological diagnosis was retrospectively reviewed using standardized criteria and the precise terminology of the World Health Organization by two pathologist physicians. At surgical excision, 6 (10%) ductal carcinoma in situ and 2 (3%) invasive carcinoma were diagnosed. The total underestimation rate was 13%. FEA was associated with atypical ductal hyperplasia in 10 (17%) cases and with lobular neoplasia in 2 (3%) at final pathology. Residual FEA was found in 14 (23%) cases. No clinical, radiological or pathological factors were significantly associated with underestimation. Our data highlight the importance of recognizing and diagnosing FEA in core needle biopsies. Thus, the presence of FEA on CNB, even in isolation, warrants follow-up excision.

Allylic oxidations of terminal olefins using a palladium thioether catalyst.

A palladium catalyst that converts terminal olefins to linear allylic acetates at lower catalyst loadings and faster reaction times than current systems is reported. This reaction can be conducted using benzoquinone as the oxidizing agent or catalytic amounts of copper and hydroquinone under one atmosphere of oxygen. Preliminary reactivity studies of pi-allylpalladium complexes under our reaction conditions do not provide results similar to those obtained in the catalytic reaction, which may suggest an alternative reaction pathway. The palladium catalyst is ligated by an aryloxyalkyl aryl sulfide, which is identified as a new ligand for homogeneous catalysis.

Effect of sulfonyl protecting groups on the neighboring group participation ability of sulfonamido nitrogen.

The addition of elemental bromine dissolved in CH(2)Cl(2) to para-disubstituted benzodiazocines where X is the same (H, CH(3), Br, OMe, NO(2)) or a different substituent as X and Y (CH(3), Br; OMe, NO(2)) has been found to proceed in most cases with competition between two pathways. While conventional trans-1,2-addition operates predominantly, electron-releasing groups also foster a ring-contraction process with ultimate 1,3-positioning of the pair of bromine atoms. The observed regio- and stereoselectivities, confirmed where necessary by X-ray crystallographic analysis, establish the capability of sulfonamide nitrogen centers to engage in neighboring group participation.

Neighboring group participation by sulfonamido nitrogen.

The ability of sulfonamido nitrogen to enter into neighboring group participation was established in two different reaction settings. The first was uncovered during the bromination of benzodiazocine 8 in dichloromethane at 0 degrees C, and the second during the base treatment of 15a en route to allene 18.