The organocatalytic
synthesis of densely substituted mono- and
bis-γ-lactams involving the Mukaiyama Mannich addition of 2,5-bis(trimethylsilyloxy)furan
to imines is described. Use of a ditoluenesulfonylimide catalyst
produces γ-lactams from monoaddition, whereas a more acidic
catalyst (triflic acid) produces fused bis-lactams from double addition.
Optimized organocatalytic conditions allow for the selective synthesis
of either desired core as well as the one-pot, multicomponent assembly
of the trisubstituted monolactams from aldehydes, amines, and bis-trimethylsilyloxyfuran.
An examination of chiral acids found these organocatalysts to be highly
active and diastereoselective in the monoaddition reaction, albeit
with no enantioselectivity.
The treatment of 2-(2-vinylphenyl)acetaldehydes or 3-(2-vinylphenyl)propanals with BF3·Et2O results in an intramolecular Prins reaction affording intermediary benzyl carbenium ions, which are then trapped by a variety of electron-rich aromatics via Friedel–Crafts alkylation. This cascade Prins/Friedel–Crafts cyclization protocol paves an expedient path to medicinally useful 4-aryltetralin-2-ol and 5-aryltetrahydro-5H-benzo[7]annulen-7-ol derivatives.
In
the presence of boron trifluoride, a variety of alkynyl sulfides
and alkynyl sulfoxides undergo tandem cross-coupling/[3,3]-sulfonium
rearrangement followed by 5-exo-dig heterocyclization.
The strategy provides concise access to novel tetrasubstituted furans
in good to high yields with 100% atom-economy efficiency. Further
derivatization of the resultant furans was feasible by utilizing the
incorporated alkylthio groups.
A new synthesis of dihydromotuporamine C (dhMotC), a synthetic analogue of cytotoxic marine alkaloid, has been achieved from inexpensive starting materials. The first stage was the preparation of cyclodecanone by sequential [2+2]‐cycloaddition of N‐(1‐cycloocten‐1‐yl)pyrrolidine with methyl propiolate and electrocyclic ring‐opening, followed by basic hydrolysis. Beckmann rearrangement of cyclodecanone oxime and several step manipulations afforded the pivotal intermediate of the N‐benzylated 11‐membered cyclic α‐vinylamine. The final synthesis of dihydromotuporamine C involved tandem nucleophilic addition with ethynyl p‐tolyl sulfone and 3‐azonia‐Cope rearrangement to form the 15‐membered aza‐macrocycle and reductive amination to install the appended spermidine‐like moiety.
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