C-C Bond Cleavage Initiated Cascade Reaction of β-Enaminones: One-Pot Synthesis of 5-Hydroxy-1H-pyrrol-2(5H)-ones

An unprecedented C(CO)-C(Ar) bond cleavage of β-enaminones has been realized under mild and transition-metal-free conditions. The cascade transformation based on this C-C bond cleavage involves 1,3-O/C migration and aerobic hydroxylation and leads to various 5-hydroxy-1H-pyrrol-2(5H)-ones with broad functional group tolerance. The application of this methodology has been showcased by preparing 5-alkoxy-1H-pyrrol-2(5H)-one derivatives and a pyrrolo[2,1-a]isoquinolin-3-one derivative.

Synthesis of 2-Alkylsulfonyl-imidazoles with Three Diversity Positions from Immobilized α-Acylamino Ketones

The synthesis of novel imidazole derivatives via immobilized α-acylamino ketones is reported in this article. The key intermediates were prepared from the Wang-piperazine resin-supported Fmoc-amino acids. After their sulfonylation with 4-nitrobenzenesulfonyl chloride (4-Nos-Cl), followed by alkylation with α-bromoketones and cleavage of Nos group, the resulting α-acylamino ketones were reacted with Fmoc-isothiocyanate. The corresponding Fmoc-thioureas were subjected to the Fmoc-cleavage and spontaneous ring-closure to imidazole scaffold. The resulting imidazole-thiones were alkylated with alkyl halides and oxidized using meta-chloroperbenzoic acid ( mCPBA). Trifluoroacetic acid (TFA)-mediated cleavage yielded the corresponding trisubstituted 2-alkylsulfonyl imidazoles in good crude purity and acceptable overall yields. In the case of sulfides, prepared from alkyl bromides, the unexpected products brominated at the C⁴ position of the imidazole were obtained.

Stereoselective tetrapyrido[2,1-a]isoindolone synthesis via carbanionic and radical intermediates: a model study for the Tacaman alkaloid D/E ring fusion

Cyclization under both radical and carbanionic conditions of N-substituted 3-phenylsulfanylisoindolin-1-one 14 containing a chiral N-tether incorporating an enoate ester as the acceptor leads to tetrahydropyrido[2,1-a]isoindolones stereoselectively. The major product 17 from carbanionic cyclization was stereoselectively desulfurized with nickel boride allowing correlation of cyclization products from both methodologies. The cyclization stereoselectivities have been rationalised using a transition-state model in which the acceptor grouping adopts a pseudoaxial configuration. This contrasts with other 6-exo-trig processes in which a pseudoequatorial configuration is normally adopted, and has been attributed to the steric influence imposed by the bulky tert-butyldiphenylsilyloxy chiral auxiliary allylic to the enoate ester. The product stereochemistries provide models for the required cis-stereochemistry of the D/E ring fusion of the Tacaman alkaloid skeleton via the relatively unexplored C-3-C-14 bond disconnection.

Unexpected facile sequential halolactamization-hydroxylation of 2, 3-allenamides with CuX(2) for the efficient synthesis of 4-halo-5-hydroxypyrrol-2(5H)-ones

[reaction: see text] 4-Halo-5-hydroxypyrrol-2(5H)-ones were synthesized from the efficient sequential halolactamization-hydroxylation reaction of 4-monosubstituted 2,3-allenamides with CuX(2) (X = Br, Cl) in high yields. Halolactamization of fully substituted 2,3-dienamide (1f) afforded 4-halo-pyrrol-2(5H)-ones.