Chemoselective preparation of ketones by the grignard reaction of N‐acylpyrazoles

Abstract

N‐Acylpyrazoles afford chemoselectively the corresponding ketones in good yields by the use of equimolar amounts of Grignard reagent. In the case of an optically active N‐acylpyrazole, optical asymmetry was retained in comparable optical yield. Ketone formation by the Grignard reactions can be regarded as an important functionalization in a synthetic loop using pyrazoles as the auxiliary compound.

Highly enantioselective Michael addition of α‐nitroacetate to α,β‐unsaturated pyrazolamide catalyzed by a bifunctional squaramide

“…The optically active β‐substituted pyrazolamides obtained via this methodology are useful materials for further synthetic manipulation. As previously reported, pyrazolamide served as a versatile ester equivalent . The typical alcoholysis occurred smoothly to provide ester 7 in 96% yield without detectable racemization (Scheme , A) .…”

“…As previously reported, pyrazolamide served as a versatile ester equivalent. [63][64][65] The typical alcoholysis occurred smoothly to provide ester 7 in 96% yield without detectable racemization (Scheme 2, A). 34,64 Free radical-mediated reductive denitration of 3aa and 3ap resulted in formation of 1,5dicarboxylic acid derivatives 8a and 8b without loss of enantioselectivity (Scheme 2, B).…”

Preparation of 2,6‐bis(l‐menthopyrzol‐3‐yl)pyridines and their catalytic activity for asymmetric diels alder reaction

“…for C 1 6 H 2 1 N 3 • 1 / 4 H 2 O : C,73.95;H,8.34;N,16.17. Found: C,73.70 H,8.12;N,16. A n a l. Calcd. for C 1 5 H 2 0 N 2 O: C,73.74;H,8.25;N,11 .…”

“…The (16) [a] 2-Pyridinyl, 2-furyl, 2-thienyl and 5-methyl-1-phenylpyrazol-3-yl groups were abbreviated as Py, Fura, Thio, and Pyra, respectively.…”

“…Otherwise, N-acylheteroaromatics such as N -acylimidazoles are utilized as the activated acyl moiety in a wide variety of organic syntheses [13]. As an analogue of these N-acylheteroaromatics, N-acylpyrazoles are easily converted into acyl derivatives by the action of nucleophiles such as alcohols [14], amines [15], Grignard reagents [16], and organozinc compounds [17] under basic or acidic conditions [18].…”