A New Class of Chiral Lewis Acid Catalysts for Highly
Enantioselective Hetero-Diels-Alder Reactions: Exceptionally High Turnover
Numbers from Dirhodium(II) Carboxamidates.
Michael P. Doyle,* Iain M. Phillips, and Wenhao Hu, J. Am. Chem. Soc.,123,
5366-5367 (2001). |
| Abstract: Although selectivities of 99% ee have been achieved in
select cases, a major drawback of this methodology has been its high catalyst
loading [substrate/catalyst (S/C) usually ? 50]. We have previously
developed chiral dirhodium(II) carboxamidate catalysts for effective and
efficient metal carbene transformations, and we now report a major extension
of their applications to hetero-Diels-Alder reactions where their operations
allow substrate to catalyst loadings of up to 10,000. |
| http://dx.doi.org/10.1021/ja015692l |
|
Epoxides and Aziridines from Diazoacetates via Ylide Intermediates.
 Michael P. Doyle,* Wenhao
Hu, and Daren J. Timmons, Organic Letters,3 (6); 933-935
(2001). |
| Abstract: An effective methodology is reported for stereospecific
epoxidation and aziridination via carbonyl ylide intermediates using rhodium(II)
acetate catalyzed reactions of phenyl- and styryldiazoacetates with aldehydes,
ketones, or imines. |
| http://dx.doi.org/10.1021/ol015600x |
|
Selectivity in Reactions of Allyl Diazoacetates as a Function of
Catalyst and Ring Size from g-Lactones to Macrocyclic
Lactones.
Michael P. Doyle* and Wenhao Hu, J. Org. Chem.,65,
26, 8839-8847 (Dec. 29, 2000 cover art). |
| Abstract: Catalytic reactions of diazoacetates tethered through
zero, one, two, and three ethylene glycol units to an allyl group have been
investigated for chemoselectivity, diastereoselectivity, and enantioselectivity.
Results from cyclopropanation, carbon-hydrogen insertion, and oxonium ylide
generation are compared from reactions of achiral and chiral catalysts of
copper(I) and dirhodium(II) carboxylates and carboxamidates. Relative to
results from intermolecular reactions of ethyl diazoacetate with allyl ethyl
ether, intermolecular reactions show a diversity of selectivities including
preference for the opposite configurational arrangement from the one preferred
in corresponding intermolecular cyclopropanation reactions. Enantioselectivities
for cyclopropanation are dependent on the catalyst ligands in a manner that
reflects divergent trajectories of the carbon-carbon double bond to the
reacting carbene center. Enantioselectivity increases as a function of ring
size with chiral copper catalysts, but the reverse occurs with chiral dirhodium(II)
carboxamidates. Mechanistic implications, including those related to the
conformation of the reacting metal carbene, offer a new dimension to understanding
of enantioselectivity in catalytic asymmetric cyclopropanation reactions. |
| http://dx.doi.org/10.1021/jo005589z |
|
Dirhodium(II) Tetrakis[methyl2-oxaazet-idine-4-car-
boxylate]: A Chiral Dirhodium(II) Carboxamidate of Exceptional Reactivity
and Selectivity.
Michael P. Doyle,*
Simon B. Davies, and Wenhao Hu, J. Chem. Soc., Chem. Commun.,867-868
(2000). |
| Abstract: A new chiral azetidinone-carboxylate ligand for
dirhodium(II) catalysts enhances reactivity toward diazo decomposition and
selectivity toward cyclopropanation enabling diazomalonates, vinyldiazoacetates,
and aryldiazoacetates to be effectively used with a dirhodium(II) carboxamidate
catalyst. |
| http://dx.doi.org/10.1021/ol005730q |
|
A New Approach to Macrocyclization via Alkene Formation
in Catalytic Diazo Decomposition. Synthesis of Patulolides A and B.
Michael P. Doyle,* Wenhao Hu, Iain M. Phillips and Andrew G. H. Wee*
Org. Lett.,2 (12), 1777-1779. (2000). |
| Abstract: Effective synthetic uses of bisdiazocarbonyl compounds
for the selective construction of diverse macrocycles, including the synthesis
of patulolides A and B, by catalytic "carbene dimer" formation are reported.
Control of stereochemistry and efficient methods for product isomerization
or kinetic isomer differentiation have been achieved. |
| http://dx.doi.org/10.1021/ol005983j |
| Reprint Request: http://pubs.acs.org/cgi-bin/download.pl?ol005983j/P45h |
|
Enantiocontrolled Macrocycle Formation by
Catalytic Intramolecular Cyclopropanation. Michael P. Doyle,*
Wenhao Hu, Brant Chapman, Alan B. Marnett, Chad S. Peterson, Justin P.
Vitale, and Sarah A. Stanley J. Am. Chem. Soc.,122, 5718-5728
(2000). |
| Abstract: Stereoselectivity in intramolecular cyclopropanation
reactions resulting in cyclopropane fusion with ten- and larger-membered
rings has been examined using chiral copper(I) and dirhodium(II) catalysts.
The influence of alkene structure and catalyst has been obtained using the
1,2-benzenedimethanol linker between the allylic double bond and diazoacetate.
Control features in the addition reaction, especially those for diastereoselectivity
and enantioselectivity, have been elucidated, and they are associated with
the metal itself or its attendant ligands that influence the trajectory
of the alkene to the carbene center. The influence of ring size, from five-
to twenty-membered rings, on stereoselectivity has been determined with
selected copper(I) and dirhodium(II) catalysts, and the changes in stereocontrol
as a function of ring size can be understood as being due to a change in
the olefin trajectory to the carbene center. Hydride abstraction from a
benzylic position accompanies addition when dirhodium catalysts are employed,
and intramolecular C-H insertion into an allylic site to form a nine-membered
ring has been observed as a major competing reaction but with negligible
enantiocontrol. The use of 1,8-naphthalene- dimethanol as a linker results
in lower enantioselectivity than does use of 1,2-benzenedimethanol. |
| http://dx.doi.org/10.1021/ja9945414 |
| Reprint Request: http://pubs.acs.org/reprint-request?ja9945414/L3zS |