10 research outputs found
Medium-Ring Nitrogen Heterocycles through Migratory Ring Expansion of Metalated Ureas
Simple benzo-fused nitrogen heterocycles (indolines, tetrahydroquinolines, and their homologues) undergo migratory ring expansion through deprotonation of their benzylic urea derivatives with lithium diisopropylamide (LDA) in the presence of N,N′-dimethylpropylideneurea (DMPU). The products of the reactions are benzodiazepines, benzodiazocines, and their homologues, with ring sizes of 8–12. The reactions tolerate a range of substituent patterns and types, and may exhibit enantiospecificity or diastereoselectivity. Considerable complexity is rapidly generated in an efficient synthesis of these otherwise difficult-to-obtain medium-ring nitrogen heterocycles
Synthesis of Isothiocineole and Application in Multi-gram Scale Sulfur Ylide-mediated Asymmetric Epoxidation and Aziridination
The synthesis of the chiral sulfide isothiocineole from limonene and elemental sulfur on multi-gram scale and its alkylation to make >50 g of the corresponding benzylsulfonium salt are described. The application of this salt to the sulfur ylide-mediated asymmetric epoxidation of aldehydes and the asymmetric aziridination of imines on a >5 g scale is demonstrated.Irish Research CouncilScience Foundation IrelandUniversity of BristolMarie-Curie Action COFUN
Synthesis of 6- and 7‑Membered <i>N</i>‑Heterocycles Using α‑Phenylvinylsulfonium Salts
A concise synthesis of stereodefined <i>C</i>-substituted
morpholines, piperazines, azepines, and oxazepines in moderate to
excellent yields (27% to 75%) is reported by reaction of 1,2- or 1,3-amino
alcohol/1,2- or 1,3-diamine with an α-phenylvinylsulfonium salt.
High levels of regio- and diastereoselectivity (from 2:1 to >20:1)
are observed through judicious choice of base (Cs<sub>2</sub>CO<sub>3</sub>) and solvent (CH<sub>2</sub>Cl<sub>2</sub>). Reactions are
performed at ambient temperature and open to air and do not require
anhydrous solvent. The deprotection of the <i>N</i>-sulfonamide
protecting groups (<i>N</i>-Ts and <i>N</i>-Ns)
is also demonstrated. Factors affecting regio- and diastereocontrol
are discussed
Synthesis of α‑Substituted Vinylsulfonium Salts and Their Application as Annulation Reagents in the Formation of Epoxide- and Cyclopropane-Fused Heterocycles
The
discovery of new methods for the synthesis of classes of potentially
bioactive molecules remains an important goal for synthetic chemists.
Vinylsulfonium salts have been used for the synthesis of a wide variety
of small heterocyclic motifs; however, further developments to this
important class of reagents has been focused on reaction with new
substrates rather than development of new vinylsulfonium salts. We
herein report the synthesis of a range of α-substituted vinylsulfonium
tetraphenylborates (10 examples) in a 3 step procedure from commercially
available styrenes. The important role of the tetraphenylborate counterion
on the stability and accessibility of the vinylsulfonium salts is
also detailed. The α-substituted vinylsulfonium tetraphenylborates
gave good to excellent yields in the epoxyannulation of β-amino
ketones (15 examples) and the cyclopropanation of allylic amines (4
examples). Hydrogenation of an epoxyannulation product proceeded with
good diastereoselectivity