Acyclic enamides

In addition to standard cyclic and acyclic enamides, the effective hydrogenation of several more unusual enamides has been reported (Fig. 24.13). A concise method for the synthesis of chiral yS-amino alcohols, amino oximes and chiral 1,2-diamines has been described by Burk et al. via the enantioselective hydroge-... 

In comparison with the hydrogenation of acyclic enamides, there are fewer sue cessful examples on the catalytic asymmetric hydrogenation of cyclic enamides... 

Isomerization of unsubstituted 1,2-dihydroazete derivatives leads to the identical compound, and therefore this reaction does not play a role for the analysis of the catalytic reaction. Stahl and Landis [43] realized the AHF ofAf-Boc-protected 1,2-dihydroazete (Scheme 4.89). Notev rorthy, the (achiral) P-formyl compound was formed at about 10 bar syngas pressure in an excess over the chiral a-formyl compound (89% ee). This regioselectivity is in contrast to that of acyclic enamides or cyclic enamides with larger ring sizes (see below). 

The reduction of enamides (62-73) has been applied primarily to the synthesis of cyclic enamines (74-76), but also to acyclic enamines (77). 

The reduction of a structurally simple acyclic tetrasubstituted enamide has been achieved [15c], also using rhodium catalysis (Scheme 9.35). 

Table 28.4 Enantioselective hydrogenation of acyclic terminal N-acyl enamides.

Figure 3.35. Scope of Rh/(5)-binap-catalyzed as5mimetric 1,4-addition of arylboronic acids to acyclic a,P-enamides.

Michael addition. ° The synthesis of the naturally occurring benz[a]anthraquinones, X-14881 (64 R = Me) and ochrotnycinone (R H) utilizes 2-phenyldithiane anion (Scheme 38), while 11-deoxydauno-mycinone was prepared using 2-methyldithiane. The formation of bicyclo[3.3.0]oct-l(5)-ene-2,6-dione utilizes 2-(2,2-diethoxyethyl)-l,3-dithiane anion. Conjugate addition of the highly stabilized anion (65) occurs readily with enamide (66), whereas the related acyclic anion (67) appears to be less reactive than the cyclic analog (Scheme 39). Conjugate addition of lithiated a-alkylthio monosulfoxide provides a new route for the synthesis of dihydrojasmone. ... 

Besides acyclic allylamines, cyclic allylamines that should yield (Z)-enam-ines, were also active substrates. In the isomerization of tetrahydropyridine derivatives 62 by the Rh-BINAP catalyst at 150 °C, the cyclic allylamide gave selectively the enamide 63. In the case of a tertiary allylamine, the isomerization occurred at 60 °C with 100% conversion. However, the corresponding (Z)-enam-ines could not be detected in the monomeric form, only the dimer 64 was isolated. Similarly, a secondary amine gave the trimer of enamine 65 in a low yield. 

This chapter describes photoreactions of nitrogen containing chromophores which are different from the principal reactions of electronically excited carbonyl compounds. Five groups of substrates were included cyclic and acyclic imines, nitriles, amine oxides, azo and diazo compounds, and enamides. 

Enamides are excellent substrates for Vilsmeier reactions, possibly because of their lower reactivity. The acyclic carbamate 44 gives the acrylaldehyde in high yield, but stereochemical integrity is lost (Eq. 36)." As in many Vilsmeier reac-... 

Peterson Oleflnation Involving Tertiary A-[Bis(trimethyl-silyl)methyl] Amides. Tertiary amide derivatives of bis(tri-methylsilyl)methylamine undergo monodesilylation, when treated with tetrabutylammonium fluoride, to form the corresponding A-(trimethylsilylmethyl) a-carbanion. Inter- and intramolecular Peterson oleflnations of this a-carbanion with aldehydes or ketones leads to acyclic and cyclic enamides. For example, the amide (1) reacted efficiently with the aldehyde (2) to afford the enamide (3, Z= 1 1) in71% yield (eq 1). Enolizable aldehydes and ketones were unsuitable reaction partners. 

An interesting approach to the preparation of enamides entailed a formal vinyl transfer from vinyl ethers (Scheme 3.122) [130]. The reaction was catalyzed by palladium complexes bearing a phenanthroline derivative as the solubilizing/stabilizing ligand. Several secondary amides including cyclic and acyclic substrates were screened, and... 

In 1992 Murahashi, Hosokawa, and co-workers described the anti-Markovnikov oxidative addition of amides and carbamates to electron-deficient olefins by applying a palladium and copper cooperative catalysis under oxygen atmosphere [41]. The proposed mechanism involved a ff-bonded palladium(II) intermediate resulting from the addition of the nucleophile to the olefin, and subsequent ) -palladium hydride elimination to yield the functionalized alkene. Interestingly, both lactams and cyclic carbamates gave predominantly the corresponding E-enamide derivatives. Acyclic amides, conversely, afforded ElZ mixtures of products. The addition of a catalytic amount (5 mol%) of hexamethylphosphoric triamide (HMPA) was found notably beneficial for the reaction of 5-membered lactams and reduced the reaction time of such particular oxidative amidations (Scheme 2). 

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