Imines and Aldehydes

Carboxylation of an amine should be possible by insertion of C02 into a Zr-C bond of a zirconaaziridine. However, treatment of 2a and 2b with C02 (Eq. 23) gave intractable white precipitates [21, 61]. Treatment of 2d with C02 gave a stable insertion product which, however, proved difficult to cleave from zirconium (Eq. 24). 

The insertion of isocyanates, isolelectronic with C02, proceeded more cleanly. Isocyanates (RNCO) with bulky R groups inserted exclusively into the Zr-C bond (Table 5) methanolysis resulted in a-amino amides 32 [21]. 

Other isocyanates inserted into the Zr-N bond as well as the Zr-C bond, resulting after workup in urea products 33 as well as the expected amides 32 [21]. The product ratio (Table 5) was independent of solvent and governed largely by the size of R. For R=i-Pr both products were formed but the major product was the amide. For small R (R=Et, Me, Bn) the major product was the urea. 

Insertion into the Zr-N bond was even more common (compare lines 3 and 12 in Table 5) when the N-silyl zirconaaziridine 2a was treated with RNCO, pre- 

Entry Zircona- aziridine RNCO Amide 32 (%) Urea 33 (%) Ratio 32/33 

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Beak and coworkers found the (—)-sparteine-complex of iV-Boc-Af-(p-methoxyphe-nyl)benzyllithium 244, obtained from 243 by deprotonation with n-BuLi/(—)-sparteine (11) in toluene, to be configurationally stable (equation 57) . On trapping 244 with different electrophiles, the substitution products 245 are formed with high ee. Efficient addition reactions with imines and aldehydes have also been reported. The p-methoxyphenyl residue is conveniently removed by treatment with cerinm ammoninm nitrate (CAN). 

Phosphonates react with aldehydes or imines to yield a-hydroxy- or a-aminoalk-ylphosphonates, respectively. These reactions can also be conducted on cross-linked polystyrene. In Figure 11.2, a sequence is outlined in which polystyrene-bound H-phosphonates are treated with imines and aldehydes. The variant in which a support-bound imine is converted into an a-aminoalkylphosphonate has also been reported... 

C. Silver-Mediated Amine, Imine, and Aldehyde Oxidation / 19... 

Dehydrogenation of Primary Amines to Imines and Aldehydes or Ketones... 

In contrast with the more reactive crotyl reagents discussed above, crotyl-silanes, -stannanes and -boronates can be prepared in isomerically pure cis and trans forms for use in imine and aldehyde addition reactions. However, isomerization of these reagents under certain reaction conditions, particularly those requiring the presence of Lewis acids, cannot be ruled out. Nonetheless, in connection with a study involving aldehyde additions, Yamamoto et al. have shown that frans-crotyltri-n-butylstannane is stable to BF.vEt20 at -78 C. ... 

Opening of 2-iminooxetanes The easy availability of 2-iminooxetanes from Lewis acid-catalyzed cycloaddition of ketene imines and aldehydes makes it desirable to find some synthetic uses. 3-Iodocarboxamides, which are generated by reaction with HI, are sources of -lactams. Remarkably little hydroxy amides is formed. 

In line with our structure-reactivity analysis delineated above, the reaction of 46a, imines, and aldehydes provided indeed 5-alkoxyoxazoles in good to excellent yields parallel to the chemistry of a-isocyanoacetamides (Scheme 15.16) [30]. The 3CR was performed with approximately equimolar quantities of the three components and reached completion between 4 and 16 h in toluene at rt or 60 °C. Both linear and a-branched aldehydes were found to be good substrates, as well as aromatic aldehydes and cinnamaldehyde. A wide range of aliphatic amines, including primary and cychc secondary amines, were suitable partners to afford the corresponding 5-aIkoxyoxazoles 50 in good to excellent yields. A concrete example is shown in Eq. (2) of Scheme 15.16. 

A wide-ranging enantio- and diastereo-selective reaction of imines and aldehydes gives anP-Mannich product. For example, PhCH2CH2CH=NTs reacts in brine with both aliphatic and aromatic aldehydes. A simple diaryl prolinol TMS ether serves as chiral catalyst A-nosyl imines can also be employed. ... 

Coordination of imines and aldehydes to Lewis acids enhances their reactivity with nucleophiles, and a wide variety of metals have been used to catalyze these types of additions. Gladysz and Templeton have studied the stoichiometric additions of main group organome-tallic reagents to aldehydes and imines. As part of these studies, Gladysz has shown that alde-... 

This kind of heterobimetallic complexes are excellent catalysts for a wide range of reactions, including epoxidation of enones, hydrophosphonylation of imines and aldehydes, and a range of asymmetric C-C bond formation reactions, involving Michael addition reaction, Diels-Alder reaction, aldol and nitroaldol reaction, etc. The alkaU metal has a profoimd effect on the catalytic property of these compounds. 

Wang W Li YL, Wang XS (2012) Highly efficient synthesis of 7-aryl-pyrano[3,4-c] pyrazolo[4,3-f]quinoline derivatives catalyzed by iodine. ARKIVOC vi 214-221 Lin XF, Cui SL, Wang YG (2006) Molecular iodine catalyzed one-pot synthesis of substituted quinolines from imines and aldehydes. Tetrahedron Lett 47 3127-3130 Jin G, Zhao J, Han J, Zhu S, Zhang J (2010) Iodine-promoted imino-Diels-Alder reaction of fluorinated imine with enol ether synthesis of 2-perfluorophenyl tetrahydroquinoline derivatives. Tetrahedron 66 913-917... 

There are two major differences between the reduction of imines and aldehydes by 2-tol imines are reduced more rapidly than aldehydes and give amine complexes as stable products (Scheme 10) [57]. Substituents on the imine affect the rate of reduction and the stability of the amine complex product. PhCH=NPh reacts with 2-lol in THF at —40°C at a rate about 150 times faster than benzaldehyde. The more basic imine PhCH=NCH2Ph reacts with 2-lol in THF at —57°C at a rate about 15 times faster than PhCH=NPh. The stability of the amine complexes depends on the basicity and steric requirements of the complexed amine. Dialkylamine complex 10 is stable to 80°C, while the less basic aryl(alkyl)amine complex 9 is stable to only 50 C. The complex of the very bulky t-Bu(PhCH2)NH complex 11 decomposed above O C. In general, amine complexes with greater number of substituents are less stable. Beller has isolated the NH3 complex 12 from catalytic systems it is unusually stable and acts as a viable catalyst precursor [58]. 

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