Isocyanocarboxylates

Another innovative approach to controlling amine-initiated NCA polymerizations was reported in 2003 by Schlaad and coworkers [20]. Their strategy was to avoid formation of NCA anions, which cause significant chain termination after rearranging to isocyanocarboxylates [11, 12], through use of primary amine hydrochloride salts as initiators. The reactivity of amine hydrochlorides with NCAs was first explored by the group of Knobler, who found that they could react... 

The gold(I) complex of a chiral ferrocenylphosphine complex promotes asymmetric aldol reactions of a-isocyanocarboxylates to form chiral oxazolines in high diastereo- and enantio-selectivities (Scheme 52).225,226 In these reactions, the analogous silver(I) ferrocenylphosphine complex also works well. 

As shown in Scheme 3-30, a,/ -unsaturated aldehyde is treated with a-isocyanocarboxylate in the presence of gold complex (S)-(R)-82 to afford, after several steps, D-eryt/zro-sphingosine derivative.53b... 

B1.2. GOLD-CATALYZED ASYMMETRIC ALDOL REACTION OF cc-ISOCYANOCARBOXYLATES... 

The catalytic asymmetric aldol reaction is tolerant of a-isocyanocarboxylates bearing an a-alkyl substituent (9a-d) as shown in Scheme 4 and Table 8B1.4 [17,18]. The enantioselectivities in the reaction with paraformaldehyde are generally moderate, with the exception of the... 

TABLE 8B1.4. Gold-Catalyzed Asymmetric Aldol Reaction of a-Isocyanocarboxylates 9 with Aldehydes (Scheme 8B1.4)... 

Asymmetric addition and insertion reactions of metal carbenes, 191-228 Asymmetric aldol reactions, 493-512,704-705 mechanism of, 496 of cr-isocyanocarboxylates, 493—502 of nitromethane, 503... 

Gold and Silver-Catalyzed Asymmetric Aldol Reactions of a-Isocyanocarboxylates... 

Keywords Isocyanocarboxylate, Aldol reaction. Gold, Silver, Ferrocenylphosphine, 3-Hydroxy-a-amino acid... 

The required a-isocyano derivatives (85) of a-amino acids are prepared from the corresponding a-formylamino acids. If (85) is a peptide derivative, no racemization is observed at the a-isocyanoacyl unit. - The preparation of chiral a-isocyanocarboxylate esters, however, is possible with phosgene or... 

The same issue is addressed in Table 8, in which reactions of nonracemic substrates are described. Regioselectivity is under steric control. All four acetates 49-52 provide mainly the ( -enantiomer82-83, probably through a common syn,syrt-n-a] yl complex. In most cases, almost 100% chirality transfer is observed. The a-isocyanocarboxylates (Table 8, entries 9, 10)84 are interesting nucleophiles for the preparation of amino acids easily obtained from the alkylated products after acidic hydrolysis. This sequence constitutes an alternative to the Schiff bases of glycine already discussed (see Table 4). Moreover, radical reduction of the isocyano group with tributylstannane yields the a-unsubstituted carboxylic esters. 

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