Harnessing Stereospecific Z-Enamides through Silver-Free Cp*Rh(III) Catalysis by Using Isoxazoles as Masked Electrophiles

Abstract

The stereospecific synthesis of Z-enamides is described in this paper. For the first time, isoxazoles have been employed as electrophiles in C−H functionalization to afford thermodynamically less stable Z-enamides utilizing salicylaldehydes in an atom-and step-economic fashion. The stereochemistry of enamides might originate from the relative disposition of atoms present in isoxazole and the intramolecular hydrogen bonding. The reaction showed excellent scope as several structurally and electronically diverse salicylaldehydes and isoxazoles reacted efficiently.

Copper‐Catalyzed Electrophilic Amidation of Organotrifluoroborates with Use of N‐Methoxyamides

“…After extensive studies, we found that the addition of LiCl dramatically enhanced the rate of the reactionw ith trifluoroborate 18 a,p roviding anilide 12 a in 62 %y ield ( Table 1, entries [12][13][14]. [10,11] Variation in the reaction solventh ad some effect on the reaction efficiency,a nd MeCN was identified as the optimal solvent( Ta ble 1, entries [15][16][17][18]. The use of 1.3 equivalents of phenyltrifluoroborate 18 a and LiCl resulted in complete consumption of N-methoxyamide 11 ( Table 1 , entry 19).…”

Iron‐Promoted Reductive Ring‐Opening and Isomerization Reactions of C4‐Alkynylisoxazoles Leading to 2‐Alkynylenaminones and Polysubstituted Furans

“…Other iron salts were screened, and FeCl 3 was the best one (Table 1, entries 1-4). The reaction conditions were further optimized by changing temperature (Table 1, entries 6,[9][10]. When FeCl 3 loading increased to 2.0 equivalent, the yield of 2 a increased to 79% (Table 1, entry 7).…”

“…[1,2] Therefore, many examples employing isoxazoles as the starting materials have been developed, including (a) reducing isoxazoles into enaminones in the presence of H 2 and metal catalyst, [3] (b) converting isoxazoles into β-keto nitriles under basic conditions, [4] (c) transforming isoxazoles into oxazole [5] or imidazole [1h] under photochemical conditions, and (d) halogen-substituted isoxazole reacting with vinyl ketone to synthesize 2azafluorenone in the presence of palladium catalyst. The isoxazoles also could react with salicylaldehyde [10] or 1,2,3-triazole [11] to produce secondary enamide or polysubstituted 3-aminopyrrole in the presence of a rhodium catalyst. The isoxazoles also could react with salicylaldehyde [10] or 1,2,3-triazole [11] to produce secondary enamide or polysubstituted 3-aminopyrrole in the presence of a rhodium catalyst.…”

“…Recently, many research groups used isoxazoles as substrates to react with alkynes in the presence of gold, platinum, Zn(OTf) 2 , and Tf 2 NH as catalysts, affording various nitrogen‐containing heterocycles. The isoxazoles also could react with salicylaldehyde or 1,2,3‐triazole to produce secondary enamide or polysubstituted 3‐aminopyrrole in the presence of a rhodium catalyst.…”

Recent Progress in the C−N Bond Formation via High‐Valent Group 9 Cp*M(III)‐Catalyzed Directed sp2 C−H Activation

“…The aldehyde sp 2 C−H or similar types of C−H bonds can also be activated under Rh(III)‐catalysis. Maji et al [38a,b] . reported C−H amination of N ‐p‐tolylsulfonyl‐(Ts‐)2‐aminobenzaldehyde and salicylaldehyde derivatives 99 by using isoxazoles 101 or anthranil 59 via the formation of five‐membered rhodacycle intermediate (Scheme 34a).…”