ABSTRACT
NHC-catalyzed nucleophilic dearomatization of alkyl pyridiniums has been achieved to generate 1,4-dihydropyridines with high enantioselectivity. This is a rare example of catalytic, asymmetric addition of a nucleophile to the activated pyridinium that prefers C-4 functionalization leading to the 1,4-dihydropyridine with high selectivity.
ABSTRACT
A small library of triazolylidene-boranes that differ only in the nature of the aryl group on the external nitrogen atom was prepared. Their reactivity as hydrogen-atom donors, as well as that of the corresponding N-heterocyclic carbene (NHC)-boryl radicals toward methyl acrylate and oxygen, was investigated by laser flash photolysis, molecular orbital calculations, and ESR spin-trapping experiments, and benchmarked relative to the already known dimethyltriazolylidene-borane. The new NHC-boranes were also used as co-initiators for the Typeâ I photopolymerization of acrylates. This allowed a structure-reactivity relationship with regard to the substitution pattern of the NHC to be established and the role of electronic effects in the reactivity of NHC-boryl radicals to be probed. Although their rate of addition to methyl acrylate depends on their electronegativity, the radicals are all nucleophilic and good initiators for photopolymerization reactions.
Subject(s)
Boranes/chemistry , Free Radicals/chemistry , Heterocyclic Compounds/chemistry , Methane/analogs & derivatives , Triazoles/chemistry , Methane/chemistry , Molecular Structure , Photochemical Processes , Polymerization , StereoisomerismSubject(s)
Azoles/chemistry , Azoles/chemical synthesis , Catalysis , Lewis Bases/chemistry , StereoisomerismABSTRACT
A concise enantioselective synthesis of (-)-paroxetine (Paxil) and (-)-femoxetine has been achieved. Key to these syntheses is a N-heterocyclic carbene catalyzed homoenolate addition to a nitroalkene followed by in situ reduction of the nitro-group to rapidly access δ-lactams.
ABSTRACT
7,7'-Dihydroxy-8,8'-biquinolyl (azaBINOL) was prepared from 2-chloroaniline in four steps: (1) the Skraup reaction, (2) Ni-catalyzed reductive coupling of 8-chloroquinoline, (3) Pd(II)-catalyzed double C-H functionalization of 8,8'-biquinolyl mediated by PhI(OAc)(2), and (4) saponification. During the third step, an axially chiral (atropos type) biaryl molecule was directly generated from an essentially achiral (tropos type) biaryl starting material.