Formylaminomethylenation of 2,3:5,6-di-O-isopropylidene-D-mannono-l,4-lactone (1 ) with ethyl isocyanoacetate (2) gave, as the major product, (€)-ethyl 3,6-anhydro-2-deoxy-2-formylamino-4,5:7,8-di-O-isopropylidene-D-manno-oct-2-enonate (3) (58%). which on hydrogenation gave ethyl 3.6-anhydr0-2-deoxy-2-formylamino-4.5 :7,8-di-0-isopropylidene-D-eryfhro-L-gluco-octonate (1 7). in almost quantitative yield. Base-catalysed equilibration of the D-eryfhro-L-gho-octonate (1 7) gave a mixture of the L-allo-, L-alfro-, L-gluco-, and L-mannoepimers [(23), (22). (17). and (19). respectively]. The configurations at C-2 and C-3 of these epimers were established by chemical and physical methods. The D-eryfhro-L-gluco-epimer (1 7) and the D-ef~hfO-L-mannO-epimer (1 9) weredegraded toethyl 3.6-anhydro-2d e oxy-2 -form y I a m i n o -4,5 -0i so p ro p y I id e n e -D -glycero -L -glucoh ep t o n a t e ( 3 7) and its D -glycero -L-mannoepimer (39), respectively. Acidic hydrolysis of compounds (1 7). (1 9). (37), and (39) gave the free amino-acids, L-2-(p-D-mannofuranosyt) -glycine (41 ), the analogous D-amino-acid (42). L-2-(~-D-tyxofuranosy~)-gtycine (43). and the analogous D-amino-acid (44). in moderate yields. In the presence of base, alcohols and thiols readily attacked the double bond of the oct-2-enonate (3) to give, for exam p I e, e t h y I (e t h y I 2d eoxy-2 -form y I a m i n o -4,5 : 7,8d i -0i so p ro p y I id e n ea -D -manno -D -glyceroo c t -3u I o -3.6-furanosid)onate and its D-manno-L-glycefo-epimer [(9) and (1 O)].THE discovery of the naturally occurring C-nucleosides and polyoxins3 has led to interest in C-glycosyl compounds 49 and carbon-carbon-linked sugar a-aminoacids.g We report a method for the introduction of a carbon-carbon linkage at C-1 of an aldonic acid lactone, leading to C-glycosyl compounds, and its use in the synthesis of glycosyl a-amino-acids. Carbon-carbon double bonds can be formed by treating a-met allated isocyanides with aldehydes and ketones in an aprotic solvent (formylaminomethylenation ' ) but attempts8 to effect reactions of lithiated ethyl isocyanoacetate with a series of esters (RC0,Et; R = alkyl, Ph, EtO, or Me,N) were unsuccessful. However, ethyl 5-isocyanomethyloxazole-4-carboxylate (7), the self-condensation product of ethyl isocyanoacetate (2), was obtained from these reactions, indicating that re-1