Ylide-substituted phosphines have
been shown to be excellent ligands
for C–N coupling reactions under mild reaction conditions.
Here we report studies on the impact of the steric demand of the substituent
in the ylide-backbone on the catalytic activity. Two new YPhos ligands
with bulky
ortho
-tolyl (pinkYPhos) and mesityl (mesYPhos)
substituents were synthesized, which are slightly more sterically
demanding than their phenyl analogue but considerably less flexible.
This change in the ligand design leads to higher selectivities and
yields in the arylation of small primary amines compared to previously
reported YPhos ligands. Even MeNH
2
and EtNH
2
could be coupled at room temperature with a series of aryl chlorides
in high yields.
Trihalide salts were found to efficiently promote photochemical dediazotizing halogenations of diazonium salts. In contrast to classical Sandmeyer reactions, no metal catalysts are required to achieve high yields and outstanding selectivities for halogenation over competing hydridodediazotization. Convenient protocols are disclosed for synthetically meaningful brominations, iodinations, and chlorinations of diversely functionalized derivatives.
The selective δ‐C(sp3)−H acetoxylation of N‐(SO2Py)‐protected amino acid derivatives has been accomplished by using palladium‐catalysis and PhI(OAc)2 (PIDA) as both terminal oxidant and acetoxy source. The distinct structural and electronic features of the SO2Py compared to more traditional carbonyl‐based directing groups is essential to override the otherwise more favourable competitive intramolecular C−H amination. The δ‐site selectivity predominates over traditionally more favorable 5‐membered cyclopalladation at competitive γ‐CH2. Experimental and DFT mechanistic studies provide important insights about the mechanism and the underlying factors controlling the chemo‐ and regioselectivity.
The hydantoin moiety
is an important structural motif
present in
various pharmaceuticals. Palladium complexes bearing electron-rich,
bulky ylide-functionalized phosphine (YPhos) ligands were found to
catalyze the arylation of N-protected hydantoins
with broadly available aryl chlorides. Selective monoarylations, sequential
diarylations, and arylation-alkylation sequences have been achieved.
In combination with stepwise deprotection strategies, this opens up
an expedient access to a wide variety of hydantoins, including derivatives
of the anticonvulsant drugs phenytoin and mephenytoin.
The selective δ-C(sp 3 )À H acetoxylation of N-(SO 2 Py)-protected amino acid derivatives has been accomplished by using palladium-catalysis and PhI-(OAc) 2 (PIDA) as both terminal oxidant and acetoxy source. The distinct structural and electronic features of the SO 2 Py compared to more traditional carbonyl-based directing groups is essential to override the otherwise more favourable competitive intramolecular CÀ H amination. The δ-site selectivity predominates over traditionally more favorable 5-membered cyclopalladation at competitive γ-CH 2 . Experimental and DFT mechanistic studies provide important insights about the mechanism and the underlying factors controlling the chemo-and regioselectivity.
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