4 research outputs found
Asymmetric Total Synthesis and Absolute Configuration Determination of (−)-Verrupyrroloindoline
The first asymmetric total synthesis
of (−)-verrupyrroloindoline
(20% overall yield in 6 steps) is described. The short approach was
enabled by Buchwald’s CuÂ(II)-catalyzed asymmetric conjugate
reduction, DMDO-triggered one-pot four-step tandem reaction, and the
first amide-selective Ir-catalyzed direct reduction of β-carboethoxy
tertiary lactam. Along with the total synthesis, the absolute configuration
of natural verrupyrroloindoline was determined as 7<i>R</i>,10<i>R</i>,11<i>R</i>
Radical Migration–Addition of <i>N</i>-<i>tert-</i>Butanesulfinyl Imines with Organozinc Reagents
A novel migration–addition
sequence was discovered for the
reaction of enantioenriched <i>N</i>-<i>tert</i>-butanesulfinyl iminoacetate <b>1a</b> with functionalized
benzylzinc bromide reagents, producing <i>tert</i>-leucine
derivatives in excellent diastereoselectivity (dr 98:2). The absolute
configurations of two new chiral centers were unambiguously assigned
by chemical transformations and X-ray crystallography. In addition,
the regio- and diastereoselectivities of this novel reaction were
both explained through the key <i>N</i>-sulfinamine intermediate <b>M6</b> generated by the <i>tert</i>-butyl radical attack
on the imine. Computational analysis of this reaction process, which
was performed at the B3LYP/6-311++GÂ(3df,2p)//B3LYP/6-31G*-LANL2DZ
level, also supported our proposed two-stage mechanism
Radical Migration–Addition of <i>N</i>-<i>tert-</i>Butanesulfinyl Imines with Organozinc Reagents
A novel migration–addition
sequence was discovered for the
reaction of enantioenriched <i>N</i>-<i>tert</i>-butanesulfinyl iminoacetate <b>1a</b> with functionalized
benzylzinc bromide reagents, producing <i>tert</i>-leucine
derivatives in excellent diastereoselectivity (dr 98:2). The absolute
configurations of two new chiral centers were unambiguously assigned
by chemical transformations and X-ray crystallography. In addition,
the regio- and diastereoselectivities of this novel reaction were
both explained through the key <i>N</i>-sulfinamine intermediate <b>M6</b> generated by the <i>tert</i>-butyl radical attack
on the imine. Computational analysis of this reaction process, which
was performed at the B3LYP/6-311++GÂ(3df,2p)//B3LYP/6-31G*-LANL2DZ
level, also supported our proposed two-stage mechanism
Total Synthesis of (−)-Sessilifoliamide J
An efficient synthesis of the <i>Stemona</i> alkaloid
(−)-sessilifoliamide J (<b>1</b>) in 12 steps and 7.7%
overall yield from the known building block <b>8</b> is presented.
The synthesis features the Corey lactonization reaction and a highly
diastereoselective α-methylation reaction to build the spiro-lactone
moiety