Synthesis of Pyridines by Carbenoid‐Mediated Ring Opening of 2H‐Azirines

Abstract

Roaming the range: The title reaction tolerates a wide range of substituents on the resulting pyridine ring using mild reaction conditions (see scheme; esp=α,α,α′,α′‐tetramethyl‐1,3‐benzenedipropionic acid). The formation of the key intermediate is catalyst‐controlled, and subsequent cyclization and oxidation affords pyridines in excellent yields. The method has been used for the efficient synthesis of polyarylpyridines.

Transition-Metal-Catalyzed Cleavage of C–N Single Bonds

“…304,305 In the catalytic cycle, the reactive Pd species 384 is generated from Pd(PPh 3 ) 4 Park et al developed a rhodium carbenoid-mediated ringopening of 2H-azirines to construct substituted pyridines 396 (Scheme 114). 308 A variety of 2H-azirines with both electronrich and electron-deficient substituents could react smoothly with a series of diazo compounds to give the corresponding pyridines 396. The experimental results indicate a 6π electrocyclization of 3-azatriene 398, which is formed by ringopening of 2H-azirines in the rhodium ylide 397, is involved in the formation of 396.…”

Rh(III)-Catalyzed Decarboxylative Coupling of Acrylic Acids with Unsaturated Oxime Esters: Carboxylic Acids Serve as Traceless Activators

“… 6 Novel approaches to diversely substituted pyridines are highly desirable, and several impressive reports highlight the recent advances in this field. 7 …”

Isothiourea-Mediated Asymmetric Functionalization of 3-Alkenoic Acids

“…CH=CHCH 2 CH 3 ),6.23 (1H, d, J 5.7, C(5)H),7.11 (2H,d, J 8.0, Ar(2,6)H); δ C(125 MHz, CDCl 3 )43.0 (C(4)), 47.6 (C(3)), 110.7 (q, J 3.5, C(5)), 120.5 (C(3)CH=CHCH 2 CH 3 ), 128.2 (ArC), 128.2 (ArC), 129.0 (ArC), 138.9 (C(3)CH=CHCH 2 CH 3 ), 166.6 (C(2));  F (376 MHz, CDCl 3 ) -72.6 (CF 3 ); m/z (NSI + ) 297 ([M+H] + , 20%); HRMS (NSI + ) C 16 H 16 F 3 O 2 + ([M+H] + ) requires 297.1097; found 297.1101 (+1.4 ppm). (3S,4R)-4-phenyl-3-((E)-styryl)-6-(trifluoromethyl)-3,4-dihydro-2H-pyran-2-one 38 Following general procedure A, (E)-4-phenylbut-3-enoic acid 16 (64.9 mg, 0.40 mmol), iPr 2 NEt (104 L, 0.60 mmol) and pivaloyl chloride (74.0 L, 0.60 mmol) in CH 2 Cl 2 (2 mL), HBTM-2.1 (2S,3R)-23 (6.16 mg, 0.02 mmol, 5 mol%), (E)-1,1,1-trifluoro-4-phenyl-3-buten-2-one 57 (80.0 mg, 0.40 mmol) and iPr 2 NEt (174 L, 1.0 mmol) for 5 minutes at −78 °C gave crude lactone (3S,4R)-38 (95:5 dr).…”