A unique stereospecific [.pi.2s + .sigma.2a] cycloaddition of

A unique stereospecific [.pi.2s + .sigma.2a] cycloaddition of tetracyanoethylene to substituted cyclopropanone acetals. Petrus G. Wiering, Jan W. Verh...
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J. Am. Chem. SOC.1981, 103, 7675-7676

7675

Table I. Degree of Racemization during Peptide Bond Formationa ~~

% racemization racemization test

peptide product

conventional coupling O.Sb (azide, 0 "C, 24 h)'"

Anderson test

Z-Gly-Phe-Gly-OEt (9)"

modified Bodanszky test''

Tfa-Ile-Gly-OEt (lo)"

10.lC*d(DCC

Izumiya test' Weygand t e s P

Z-Gly-Ala-Leu-OBzl (11)'' Tfa-Val-Val-OMe (12)''

Oe (azide, 0 "C, 72 h)I3