A systematic density functional theory level investigation of differently substituted pyridinium methylides was carried out to determine the role of C(ylidic) lone-pair-associated hyperconjugative and negative hyperconjugative interactions in deciding conformational preferences. Deviation from the coplanar orientation of the carbanionic center with the pyridine ring and its substituent dependence has been found to correlate well with the relative opportunities for conjugative and negative hyperconjugative interactions of a ylidic moiety with different substituent groups present at the ylidic carbon. The contribution of individual n-->pi* conjugative, n-->sigma* negative hyperconjugative, and sigma-->pi* hyperconjugative interactions in a particular conformation of pyridinium dichlorophosphinomethylides was assessed from donor-acceptor stabilization energies, as obtained from natural bond orbital (NBO) analysis. The relative extent of conjugative and negative hyperconjugative interactions with the substituents present at the ylidic carbon plays an important role in permitting the delocalization of ylidic charge into the pyridine ring, thereby controlling the relative orientation of the latter with the carbanionic plane.

NOTES 557 ton and Overhoff state: "Very numerous attempts were made to condense phthalimidohalogenoacetones with ethyl sodiochloromalonate and indeed with ethyl sodiomalonate itself under various conditions, but all were in vain. The halogenoacetones reacted exothermically with the sodiomalonates with rapid elimination of the sodium halide, but normal condensation did not occur, the products consisting for the most part of highly pigmented resins."The coupling of III with sodium diethylmalonate was studied in several solvents under various conditions and was found to yield several products. At refluxing temperature in alcohol sodium bromide was formed, but attempts to crystallize a product from alcohol, ether, and chloroform failed. A very small amount of material was crystallized from acetone, but was not studied further. When III was added as a solid to an alcoholic solution of sodium diethylmalonate at room temperature the reaction mixture crystallized spontaneously.The material (obtained in high yield, but not the desired product) was recrystallized from 95% ethanol in which it is only slightly soluble, m.p. 278-279°. A sample was prepared for analysis by recrystallization from W,W-dimethylformamide by addition of water and also from alcohol-water.The analysis suggested phthalimide (calculated

The m-phosphorylanilides 2 are available from anilides 1 by the Atherton-Todd reaction; the selective ortho-lithiation of the oЈ-methyl-protected phosphorylpivalanilide 2b with tBuLi proceeded in high yield in the presence of ClSiMe 3 . The ortho-lithiation is followed by rapid 1,3-migration of the PO 3 Et 2 group to yield the phosphonoanilide cis/trans-3b. This compound mainly reacts with excess LiAlH 4 by reductive cyclization to form the 4-hydroxy-1H-1,3-benzazaphosphole 6. The lithiation of the oЈ-unprotected phosphoryl-

A site-selectivity model, based on the Fukui function as a local reactivity descriptor, has been applied to 1,2-disubstituted pyridinium ions incorporating two competing sites of similar reactivity, i.e., 1-methylene and 2-methylene, which may undergo deprotonation depending on the nature of substituent present on these moieties. Applicability of the local HSAB rule, in context with the Li-Evans' generalized HSAB principle suggesting the hard-hard interactions to be controlled by minimum Fukui function, has been illustrated. Global and local reactivity descriptors have been computed by carrying out DFT calculations at B3LYP/6-31++G** level using Mulliken and NPA methods for charge analysis. A comparison with the calculated deprotonation energies involving two sites indicates that the observed site selectivity in differently substituted pyridinium ions is better explained by the Li-Evans rule of minimum Fukui function for hard-hard interactions.