Synthetic Organic Reactions Mediated by Sodium Hydride

Sodium Alkyl(trimethylsilyl)amides: Substituent- and Solvent-dependent Solution Structures and Reactivities

The preparation of sodium isopropyl(trimethylsilyl)amide (NaPTA), sodium (1-phenylethyl)(trimethylsilyl)amide (NaPETA), sodium tert-butyl(trimethylsilyl)amide (NaBTA), and isotopologues [15N]NaPTA and [15N]NaBTA are described. Solution structural studies using a combination of 29Si NMR spectroscopy, the Method of Continuous Variations, and density functional theory computations provided insights into aggregation and solvation in a range of solvents including toluene, N,N-dimethylethylamine, triethylamine, MTBE, THF, 1,2-dimethoxyethane (DME), diglyme, N,N,N',N'-tetramethylethylenediamine (TMEDA), N,N,N',N'-tetramethylcyclohexanediamine (TMCDA), N,N,N',N″,N″-pentamethyldiethylenetriamine (PMDTA). 12-crown-4, 15-crown-5, and 18-crown-6 revealed solvent- and substituent-dependent dimer-monomer mixtures with affiliated solvation numbers. Complexation of the three crown ethers documented both crown and substituent dependencies. Qualitative studies of reactivity showed a variety of reactions of NaPETA. Aminolysis of methyl benzoate with dialkylamines mediated by NaPTA afforded high yields of benzamides. Quantitative rate studies of aminolysis of methyl benzoate by NaPTA revealed a 47,000-fold range of rates. Detailed rate studies in toluene and THF showed dimer-based mechanisms. The role of primary- and secondary-shell solvation by THF is discussed, including nuances of methods used to separate the two contributions. PMDTA-solvated NaPTA monomer reacts as a monomer whereas bis-diglyme solvated monomer reacts as a dimer. Rate studies exploring the structure-reactivity correlations of the three crown ethers show mono- and bis-crown-based pathways in which 15-crown-5─the crown ether often said to be of choice for sodium─was decidedly inferior as an accelerant.

Stereochemistry in All Its Shapes and Forms: The 56th Bürgenstock Conference

Acknowledging the crucial role of stereochemistry in fields as diverse as total synthesis, synthetic methodology, spectroscopy, and the study of the origin of life, the 56th SCS Conference on Stereochemistry, better known as the BÃ1/4rgenstock Conference, brought together a diverse range of chemistry expertise in Brunnen, Switzerland.

Sodium Isopropyl(trimethylsilyl)amide: A Stable and Highly Soluble Lithium Diisopropylamide Mimic

The preparation, structure, physical properties, and reactivities of sodium isopropyl(trimethylsilyl)amide (NaPTA) are described. The solubilities at room temperature range from n-heptane (0.55 M), n-hexane (0.60 M), toluene (0.65 M), MTBE (1.7 M), Et₃N (3.2 M), and THF (>6.0 M). The half-life to destruction in neat THF is >1 year at 25 °C and 7 days at 70 °C, which compares favorably to 2.5 months and 1.5 days, respectively, for LDA in neat THF. This study focuses on NaPTA in THF. ²⁹Si NMR spectroscopy shows exclusively a mixture of cis and trans stereoisomeric dimers in 0.10-12 M THF in hexane. Density functional theory (DFT) computations suggest that the pK_b is intermediate between dimeric sodium diisopropylamide (NaDA) and dimeric sodium hexamethyldisilazide (NaHMDS). Metalations of arenes, epoxides, ketones, hydrazones, alkenes, and alkyl halides show higher reactivities than LDA (k_NaPTA/LDA = 1-30). While the rates of arene metalation are high, the lower pK_b of NaPTA limits the substrates. Metalation of pseudoephedrate-based carboxamides to form disodiated Myers enolates solves several challenging technical problems.

Partial reductions of carboxylic acids and their derivatives to aldehydes

Recent advances in partial reductions of inert carboxylic acids and their derivatives to active aldehydes are reviewed.

Molecular Main Group Metal Hydrides

This review serves to document advances in the synthesis, versatile bonding, and reactivity of molecular main group metal hydrides within Groups 1, 2, and 12-16. Particular attention will be given to the emerging use of said hydrides in the rapidly expanding field of Main Group element-mediated catalysis. While this review is comprehensive in nature, focus will be given to research appearing in the open literature since 2001.