Transcript Presentation_21

Shimizu, Yohei; Shi, Shi-Liang; Usuda, Hiroyuki; Kanai, Motomu; Shibasaki,
Masakatsu. Catalytic Asymmetric Total Synthesis of ent-Hyperforin.
Angewandte Chemie, International Edition (2010), 49(6), 1103-1106, S1103/1S1103/75.
Chiral bisoxazolidinone ligands
(BOX ligands)
Diels Alder Reaction
The Diels Alder Reaction constitutes a very powerful method for the
generation of a six membered ring.
A wide variety of dienes and dienophiles are possible. Most commonly, the
dienophile possesses an electron withdrawing group, as shown in the
examples below.
MOM ethers as protecting
groups for alcohols
MOM = Methoxymethyl
LDA = lithium diisopropylamide,
Diisopropylamine pKa = 36
HMPA = hexamethylphosporamide
A polar solvent
Isoprene
The Claisen Rearrangement
Like the Cope Rearrangement, this is an electrocyclic
process, categorized as a 3,3-sigmatropic rearrangement
Hydroboration-oxidation sequence accomplishes antiMarkovnikov addition of water to the carbon-carbon
double bond
Link
Disiamylborane is a very hindered organoborane,
with high selectivity for the terminal position of a
terminal double bond.
CSA = camphorsulfonic acid, pKa = 1.2
Markovnikov’s Rule
The regioselectivity of the Markovnikov Rule is caused,
mechanistically, by the tendency to form the more stable
carbocation, during the initial electrophilic addition to the
double bond, as shown above.
The Swern Oxidation
Mechanism of the Swern Oxidation
Reagents which result in an ‘activated’
form of DMSO
Hoveyda-Grubbs 2nd generation catalyst =