New method for the preparation of 4-acylpyrazoles. Reaction of C(.alpha.),N dianions of phenylhydrazones with acid chlorides

1-Azaallylic Anions in Heterocyclic Chemistry

“…78 The γ-trimethylsilyloxy-R-chloroketimines 175 cyclized with alcohols to afford cis-2-alkoxy-3-aminotetrahydrofurans 177 in a stereospecific way after treatment with base (Scheme 36). 79 The mechanism was explained in terms of two possible routes involving either a trans-2-amino-3-chlorotetrahydrofuran, (184) with lithium diisopropylamide produced the 3,3-dichloro-1-azaallylic anion 185, which reacted with 2-bromoethyl trimethylsilyl ether (174), resulting in the R,R-dichloroimine 186, the acidic hydrolysis of which gave 3,3-dichloro-2-hydroxy-2-phenyloxolane 187 (Scheme 38). 80 Using the same methodology, the synthesis of the marine natural product laurencione (194) was accomplished.…”

“…170,171 In this matter, one-pot acylation reactions of N-phenylhydrazone dianions 552 and subsequent acid-catalyzed ring closure furnished pyrazoles 554 (Scheme 107, route a). [172][173][174][175] Following the same condensation-cyclization process, starting from N-unsubstituted hydrazone, 1H-pyrazoles were synthesized. 176 In the same way, condensation of 1-azaallylic anions 552 with aldehydes and subsequent treatment with acid gave 2-pyrazolines 555 (Scheme 107, route b).…”

One-Pot Cyclizations of Dilithiated Oximes and Hydrazones with Epibromohydrin. Efficient Synthesis of 6-Hydroxymethyl-5,6-dihydro-4H-1,2-oxazines and Oxazolo[3,4-b]pyridazin-7-ones

“…The cyclization of hydrazone dianions with esters, acid chlorides, and nitriles has been reported to give pyrazoles. Pyrazolines are available by cyclization of hydrazone dianions with α-halo ketones. , Reactions of hydrazone dianions have been used for the synthesis of 1,2,3-thiazoles . Recently, we have reported the synthesis of functionalized 1,2-oxazines by cyclization of oxime dianions with epibromohydrin .…”

Five‐Membered Heterocycles: 1,2‐Azoles. Part 1. Pyrazoles

“…The reaction of dilithiated hydrazone anions with electrophiles (esters [125][126][127][128][129], acyl chlorides [128,130], nitriles [131], amides [128], a-haloketones [128], aldehydes [132] or diethyl carbonate [133]) followed by acid-catalyzed ring closure furnishes adequately functionalized pyrazoles (Scheme 8.21).…”