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Di-t-butyl dicarbonate and one of its dithiol analogs, practical methods of preparation for which are given, react with amino-acid esters to form the N-t-butoxycarbonyl (t-BOC) derivatives and the thiol analogs in good yield under mild conditions. The thiol analogs are stable to acidic conditions, which rapidly remove the t-BOC group itself. t-Butyl trimethylsilyl carbonate forms a (CHa)aSi ether from a M-thiol-t-BOC serine methyl ester. The N-thiol-t-BOC group can be removed from the -NHCOSR (R = t-butyl) by heating with peroxide-acetic acid. Action of the dicarbonates described above has not been attended by racemization in the cases examined. The two dicarbonates may be useful as agents for selective blocking and deblocking of amino or other groups.Recent studies (1, 2) in this laboratory have made the tricarbonates 1 and 2 readily available. From them, without isolation of the tricarbonates if desired, the corresponding dicarbonates 3 and 4 are readily prepared by treatment with tertiary amines or by mild heating (3). 1,X= 0 3,X 0 2,X =S 4,X= S R = t-butyl The ready availability of the sulfur and oxygen dicarbonates (for nomenclature, see ref. 2.) suggested that their behavior with a-amino acids should be studied, because the expected reaction (4, 5) would lead to the t-butoxycarbonyl (t-BOC) derivatives, or their sulfur analogs (thiol-t-BOC); the t-BOC group is a standard protecting group for the amino group in peptide syntheses. The reaction of 3 and 4 should allow synthesis of such derivatives under mild conditions, and might have useful applications in selective alteration of enzymes or proteins.The expected reaction (4, 5) took place readily; the aminoacid ester hydrochloride was usually used, neutralized with bicarbonate, and heated briefly in tetrahydrofuran (THF) or chloroform to give the product in good yield. Free glycine was also used successfully.

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A study of twelve examples of the Schonberg rearrangement of diaryl thioncarbonates to diaryl thiolcarbonates has shown that the reaction is favored by electron-withdrawing groups in the 07th and para positions. It is suggested that the reaction involves a cyclic transition state, with a nucleophilic attack of the thion sulfur on the aromatic nucleus. The similarity of this rearrangement to the Smiles, Chapman and Stevens rearrangements, and to reactions involving a shift from oxygen to sulfur, is discussed.The rearrangement of diaryl thioncarbonates I to diaryl thiolcarbonates I1 which was discovered by Schonberg2 offers a way of converting phenols to S 0 II A /I ArOCOAr + ArOCSAr I I1 t iH20, OH-2ArOH + S = CC12 ArOH + ArSH

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