Abstract:COMMUNICATIONS a b C 2a 2c I 13 14 tlmin _ _ t 8 3 mizd 32 50 100 150 m l z -Fig. 3. Gaschromatograms (chiral column) [I71 of2a--d (a)and of fragment C (b): mass spectra of 2a (c) and fragment C (d). polycyclic pol yether Me 113 1 1b5 HO Scheme 4. The two side chains of MTX and the correct absolute configuration (the complete structure of the polycyclic polyether is given i n the preceding communtcation [I]).
“…Barmann and Schinzer 368 have reported for the first time the enantioselective preparation of planar-chiral η 2 -manganese complexes and their use in alkylation and asymmetric aldol reactions. By using this method of asymmetric C−C bond formation, they have obtained derivatives in high optical purity.…”
Section: Asymmetric Aldol Couplings With Aldehydesmentioning
The cyclopentenone unit is a very powerful synthon for the synthesis of a variety of bioactive target molecules. This is due to the broad diversity of chemical modifications available for the enone structural motif. In particular, chiral cyclopentenones are important precursors in the asymmetric synthesis of target chiral molecules. This Review provides an overview of reported methods for enantioselective and asymmetric syntheses of cyclopentenones, including chemical and enzymatic resolution, asymmetric synthesis via Pauson-Khand reaction, Nazarov cyclization and organocatalyzed reactions, asymmetric functionalization of the existing cyclopentenone unit, and functionalization of chiral building blocks.
“…Barmann and Schinzer 368 have reported for the first time the enantioselective preparation of planar-chiral η 2 -manganese complexes and their use in alkylation and asymmetric aldol reactions. By using this method of asymmetric C−C bond formation, they have obtained derivatives in high optical purity.…”
Section: Asymmetric Aldol Couplings With Aldehydesmentioning
The cyclopentenone unit is a very powerful synthon for the synthesis of a variety of bioactive target molecules. This is due to the broad diversity of chemical modifications available for the enone structural motif. In particular, chiral cyclopentenones are important precursors in the asymmetric synthesis of target chiral molecules. This Review provides an overview of reported methods for enantioselective and asymmetric syntheses of cyclopentenones, including chemical and enzymatic resolution, asymmetric synthesis via Pauson-Khand reaction, Nazarov cyclization and organocatalyzed reactions, asymmetric functionalization of the existing cyclopentenone unit, and functionalization of chiral building blocks.
“…The absolute configuration of 4a was established by the X-ray crystallographic analysis of the less polar diastereomer (4 S )- 4a (Figure ). Similarly, 5-methyl-2-[(2,4,6-triisopropylphenyl)sulfinyl]-2-cyclopentenone ( 4b ) was prepared from 5-methyl-2- cyclopentenone ( 1b ) 9a. The absolute configuration of 4b was determined as shown in Scheme .…”
Section: Resultsmentioning
confidence: 99%
“…The absolute configuration of 4b was determined as shown in Scheme . Reduction of the more polar diastereomer 4b with diisobutylaluminum hydride and subsequent syn-elimination of the sulfenic acid by heating under reflux in CCl 4 afforded (5 R )-5-methyl-2-cyclopentenone ( 1b ), the structure of which was determined by comparison of the optical rotation with the value for the known compound 9b 1 1 Chem 3D representation of the X-ray structure of (4 S )- 4a . …”
Addition of alkyl radicals to a diastereomeric mixture
of (4R)- and
(4S)-4-methyl-2-[(2,4,6-triisopropylphenyl)sulfinyl]-2-cyclopentenones gave the diastereomerically
pure addition product derived
from the (4R)-isomer, while the (4S)-isomer
remained unreacted. The tert-butyl radical
addition
to a diastereomeric mixture of (5R)- and
(5S)-5-methyl-2-[(2,4,6-triisopropylphenyl)sulfinyl]-2-cyclopentenones also gave the diastereomerically pure addition product.
These results show that
(4R) and (4S) or (5R) and
(5S) diastereomers were kinetically separated in the radical
β-addition.
The 1,2- and 1,3-steric interactions in the radical addition to 4-
or 5-methyl-2-cyclopentenones were
also examined.
“…Recently, these complexes were prepared in enantiomerically pure form by the sequence illustrated in Scheme 19. 45 Bromo alcohol 24 was obtained in 94% enantiomeric excess by resolution of the racemate with lipase and, after removal of bromine, this compound was complexed diastereoselectively with the manganese fragment as shown. The original chiral centre was then removed via an oxidative procedure (TPAP) which, remarkably, left the transition metal untouched.…”
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