M. Sprecher

The Schmidt Reaction of Dialkyl Acylphosphonates

The scope of the Schmidt rearrangement of ketones has been extended to dialkyl acylphosphonates (11a-111). Surprisingly, it was found that 11a-11dand 11g, in which the acyl moiety was benzoyl alone or benzoyl bearing an electron-attracting or mildly electron-releasing substituent, yielded an overwhelming portion of products resulting from C-to-N migration of the aryl group (N-arylcarbamoylphosphonates, 12, and N-arylformamides, 15). Contrariwise, the arenecarbonylphosphonates, which carry a powerful electron-releasing p-alkoxy group, yielded products resulting from phosphonate group migration from C to N or elimination (dialkyl N-arenecarbonylphosphoramidates, 13, and arenecarbonitriles, 17, respectively)

Structure and conformation of heterocycles—VIII : Peripherally substituted 1,4,5,8-tetraoxadecalins

Abstract The synthesis of the title compounds was examined and a mechanistic scheme was put forward, which accounts for their formation along with higher substituted by-products and with the corresponding bidioxolan-2-yl isomers. Chemical correlation between two members of the series, trans -2,3-dicarbomethoxy- and trans-2, 3 - dimethyl - tetraoxadecalin, was performed. All stereoisomeric 2,3 - dicarbomethoxy -1,4,5,8- tetraoxadecalins were prepared and chemically equilibrated. The free energy differences at 65° between them were thus obtained. This led to an evaluation of the conformational free energy of the carbomethoxy group in dioxanes, ΔGCO2Meo. = 0.38 kcal/mole. Dynamic conformational analysis by variable temperature NMR measurements on cis - 2, 3 -dicarbomethoxy - anti -cis - 1, 4, 5, 8- tetraoxadecalin led to a ring inversion barrier of AG193≠ = 10.0 kcal/mole.

Barriers to rotation about the amide (N–CO) and sulphenamide (N–S) bonds in methyl N-arylsulphenyl-N-benzylurethanes. A simple molecular orbital model to explain substituent effects on sulphenamide rotational barriers

Barriers to rotation about both the N–S and N–CO bonds have been measured in a series of substituted methyl N-arylsulphenyl-N-benzylurethanes, XC6H4SN(CH2C6H5)CO2CH3, by analysis of the temperature dependent n.m.r. spectra of the benzyl methylene protons. N–S Torsional barriers increase linearly with increasing electron demand of the substituents (σ– substituent constant), while N–CO barriers are substituent independent. This result is inconsistent with a mechanism for S–N torsion involving (p–d)π conjugation between the nitrogen lone pair and sulphur. An alternative rationale is proposed, based on a simple perturbational molecular orbital model. Application of the model to various experiments is discussed, with the conclusion that it adequately rationalizes all the currently available (and sometimes inexplicable) results on sulphenamides.

Synthesis of enol sulphonates from carbonyl compounds

Sulphonic anhydrides and dimethylformamide convert ketones and aldehydes into enol sulphonates, which are generally relatively stable towards acids and bases but regenerate the carbonyl compounds by O–S bond cleavage on more vigorous treatment.