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to be more stable than either 6b or 6b'. Since the conformation 6b" has a dimethylamino group in a pseudoequatorial position, the observed increase in basicity is not unreasonable.The dissociation constant of the tertiary amine 6c is quite similar to that of 6b, suggesting that the two bases may have similar conformations. The basicity of the tetramethyl derivative 8b is less than that of 8a. In 8b, the axial methyl groups at the 2,6-positions may hinder solvation of +NH(CH3)2, and hence the basicity of the amino group may be reduced. Experimental Section4-Aminooxanes la,b,d,e, 2a,b,d,e, and 3 were prepared as reported.9 Preparation of compounds lc,f-n, 2c,f-n, 4a-f, 5a-f, 6a-c, 7a-c, and 8a, will be reported elsewhere.10General Procedure for the Measurement of Dissociation Constants.1 234 The amines were purified by either repeated crystallizations or distillation under reduced pressure. Methyl Cellosolve (2-methoxyethanol) was purified initially by distillation over quick lime and subsequently by fractionation using a Dufton column [bp 124 °C (760 mm)]. Distilled water, free from carbon dioxide, was prepared, and 80% 2-methoxyethanol was used as the solvent.The amine (about 15 mg) was dissolved in 80% 2-methoxyethanol (25 mL). While the solution was stirred under nitrogen, 0.05 N hydrochloric acid was added dropwise from a buret that could be read to 0.005 mL. The pH values were measured in a pH meter, precalibrated with buffers at pH 4.0 and 9.2 with a glass electrode and a saturated calomel electrode as the reference electrode. All measurements were made at 27 ± 0.1 °C. The equivalence point was determined from a plot of pH against volume of HC1 added. An average value (pKa) of one-fourth, one-half, and three-fourths neutralizations was taken, and at least two independent titrations were carried out on each compound. The pH meter was an Elico Digital pH meter (Model LI-120) with an accuracy of ±0.01 pH units.Acknowledgment. We thank Professor D. K. P. Varadarajan, Principal, PSG College of Arts and Science, Coimbatore, India, and Mr. G. Varadaraj, Managing Trustee, PSG Institutions, Coimbatore, India, for the constant encouragement and financial support. P.K.S. thanks the CSIR, New Delhi, India, for the award of a Junior Research Fellowship. K.D.B. thanks the College of Arts and Science Office of Research for partial support in the form of salary. K.D.B. also gratefully acknowledges partial funding from National Science Foundation in the form of Department Grants to purchase the XL-100 (15) NMR spectrometer (G.P. 17641) and the TT-100 PFT accessory (CHE-76-05571).

13C Substituent chemical shifts of the carbonyl sites in the side-chains of meta-and para-substituted benzenes of the type XC,H,COZ have been measured. Analysis of this data using the dual substituent parameter method shows that inductive effects are predominant, The reverse inductive contribution observed is explained in terms of a xpolarization mechanism. Critical support for this mechanism is obtained from additional series where the carbonyl is complexed with Lewis acids. The concepts of ' extended ' and ' localized ' n-polarization are discussed. -2.23 -0.

N-Methyl amino acids occur in many natural products. Experimental strategies are presented for a unified approach to the synthesis of N-methyl derivatives through 5-oxazolidinones of the 20 common l-amino acids. The amino acids with reactive side chains that required protecting groups or devoted syntheses for side chain construction for N-methylation to proceed included serine, threonine, tyrosine, cysteine, methionine, tryptophan, asparagine, histidine, and arginine. The studies have provided improved methods for the preparation of N-methyl serine, threonine, and tyrosine. All 20 of the common l-amino acids are now available in suitable forms for solid or solution-phase peptide synthesis.

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