H-phosphonates, H-phosphinates and secondary phosphine oxides may be preligands, and are important building blocks in the synthesis of pharmaceuticals, pesticides, and P-ligands. The prototropic tautomerism influenced by substituent effects plays an important role in the reactivity of these species. The main goal of our research was to study the tautomerism of the >P(O)H reagents by means of computational investigations applying several DFT methods at different levels. We focused on the effect of implicit solvents, and on explaining the observed trends with physical chemical molecular descriptors. In addition, multiple reaction pathways incorporating three P-molecules were elucidated for the mechanism of the interconversion.

The resolution methods applying (-)-(4R,5R)-4,5-bis(diphenylhydroxymethyl)-2,2-dimethyldioxolane ("TADDOL"), (-)-(2R,3R)-α,α,α',α'-tetraphenyl-1,4-dioxaspiro[4.5]decan-2,3-dimethanol ("spiro-TADDOL"), as well as the acidic and neutral Ca(2+) salts of (-)-O,O'-dibenzoyl- and (-)-O,O'-di-p-toluoyl-(2R,3R)-tartaric acid were extended for the preparation of 1-n-butyl-3-methyl-3-phospholene 1-oxide in optically active form. In one case, the intermediate diastereomeric complex could be identified by single-crystal X-ray analysis. The absolute P-configuration of the enantiomers of the phospholene oxide was also determined by comparing the experimentally obtained and calculated CD spectra.

The earlier described a 3‐methyl‐1‐phenyl‐3‐phospholene 1‐oxide (1) → 6,6‐dichloro‐1‐methyl‐3‐phenyl‐3‐phosphabicyclo[3.1.0]hexane 3‐oxide (2) → 4‐chloro‐1‐phenyl‐1,2‐dihydrophosphinine 1‐oxide (3) → 4‐chloro‐5‐methyl‐1‐phenyl‐1,2,3,6‐tetrahydrophosphinine 1‐oxide (4) reaction sequence was investigated from the point of view of preparing optically active intermediates/products (2–4). In principle, both the resolution of the corresponding racemic products and the transformation of the optically active starting materials are suitable approaches for the preparation of optically active six‐membered P‐heterocycles (2–4). Racemization occurred during the dichlorocyclopropanation reaction of (S)‐3‐methyl‐1‐phenyl‐3‐phospholene 1‐oxide ((S)‐1), but the thermolytic ring opening of (−)‐2, and the selective reduction of α,β‐double bond of (−)‐3 did not cause the loss of optical activity. First in the literature, the resolution of a 3‐phosphabicyclo[3.1.0]hexane 3‐oxide (2) and a 1,2,3,6‐tetrahydrophosphinine 1‐oxide (4) was elaborated. © 2013 Wiley Periodicals, Inc. Heteroatom Chem 24:179–186, 2013; View this article online at http://wileyonlinelibrary.com. DOI 10.1002/hc.21080

A simple, efficient, and economical method based on the combination of the exceptional behavior of o,o'-dibenzoyl- or o,o'-di-p-toluyl-(2R,3R)-tartaric acid in chiral recognition processes, and the coordination ability of calcium or magnesium ion was developed for the resolution of phospholene oxides 1. The calcium or magnesium salt of (-)-o,o'-dibenzoyl-(2R,3R)-tartaric acid 2,4-6 or calcium hydrogen (-)-o,o'-di-p-toluyl-(2R,3R)-tartrate 3 may form crystalline diastereomeric coordination complexes with the appropriate antipode of substituted 3-phospholene oxides 1 that makes possible efficient resolutions. Optically active phospholene oxides 1 were prepared directly by simply crystallization and digestion of the corresponding diastereomeric complexes so formed. Thermal behavior of the crystalline diastereomeric complexes was studied by simultaneous TG/DTA. The novel method may be of more general value in respect of the resolution of tertiary phosphine oxides.

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