A&rut-
The re+.ion romolcdcItea 2 (r/u N-acylimiao acetates 3 ) with of .N-ic+uaino-2-b r order mued CuprUes, triaWh ilyl Otb0I Oth4n Md bdicubonyl compo Jze kqd8tqrw#tyofa-aatino A? dorindveq. Their conveoioa into the fr@ kmi8o acida aa k cOtlv0anbatly CUrM OUt by the tuI Of I-butyl protoc&a. In an of the N--l Wmpoua& clam of Abe Drotectin8 group md optical raolutioa aa be achkwed ia one st6p by has renaJ WYkW. Electrophilic glyciae equiv8ktll are enjoyinp incre8sin) popu~lity SitH 8en Ishoi's pionbeling investigations . '1 In recent yew wvrml of them compounds have ken introduced for the synthesis of aamino acids e.g. N-rcylimioo amlaaatns'~. N-acylimiao ~cdtat&~), a-acetoxylated N-rrylidene glycinatese) and chiral heterocyclea '4 The discovery that a variety of N-rcylamino acetates 1 an be . bromineted smoothly to yield the a-bromo duivativw 2 has nrrde thh -up of 8lyciaa equinlentr easily avaikblc'~g~lO). Gn treatmeat of 2 with (crl. unkbq or an excuse of or~urolaatrllic qena, hi@t4y rsrtive o-acylimino acotatw 3 I') are formed in situ which react with a au&or of C-nucleophila to yield N-protected o-amino acid es&n. 0 Brq or NBS R1J+W2R' -H hr 1. C-nudeophR_ =Mu' 2 H30° .x H3N CO; R' MO MO Cf3 Ph Ph Ph OBut R' Me But Et Ma Et (+)-mm6ji But This reaction has been carried out so far with Gri&aard re8grats8*'l) and e&d"). By virtue of its sterically shielded arbonyl group, aad thr ease of d@totOCtiOa after C-C-bond formrtioa. r-butyl 2bromo-2-(r-butoxyarbonylxmino~te 21 is the ~tapooad of choti for the syatbsria of fred uniao acid?*"). We now report on recent progrus in the IIBD of N-rcylimibo acetate for a-rmino Icid ryatbstb. 5403 5404 T. B-m CI al. In many cases the reaction of N-rcylimino acetates with aliphatk Grimd reagenta occun only in modest yield. We therefore tested l vubty of altentative organou~~tUk raagouts, amon which the higher order mixed cuprates,. R,Cu(CN)Li,, devebped by Up&&t and coworkers") gave by far the best results. This ix in agreement with the experience of O'Donnell@) and Wi/Iianu') with other ebctrophilic llycine equivalents. Reaction of two equivaknts of oupmte reuent with 006 8qrrinlrrt,.af 2-acyhmino-2-bromoacmte in THF at -78'C km& to the formation of the &aired aa~ino acid derivativea in good ykki (Table I). In thh way l ikyi, rlkenyl and rryl 8roupr an b transferad to the N-rcylimino acetates 3 . _
Table 1.