Methodologies in Asymmetric Catalysis - American Chemical Society

Chapter 1

Chiral Dirhodium(II) Carboxamidates for Catalytic Asymmetric Synthesis

Downloaded by ANDREWS UNIV on July 21, 2013 | http://pubs.acs.org Publication Date: July 4, 2004 | doi: 10.1021/bk-2004-0880.ch001

Michael P. Doyle Department of Chemistry, University of Arizona, Tucson, AZ 85721

Chiral dirhodium(II) carboxamidates are remarkably effective catalysts for a variety of asymmetric transformations, especially those of diazoacetates and diazoacetamides, but also including Lewis acid catalyzed reactions. High selectivities are achieved even with low catalyst loadings, and polymer-bound catalysts are effective for multiple recovery and reuse. Cyclopropanation, carbon-hydrogen insertion, and ylide reactions have received considerable attention, and high enantiocontrol has been achieved, especially in intramolecular reactions.

The Catalysts Dirhodium(II) carboxamidate catalysts are constructed from dirhodium(II) acetate by ligand replacement (eql)(/-3). Since the amide ligands are more

4LH + Rh (OAc) 2

4

*ff

v

r e f l u x

»

Rh L + 4HOAc (trapped with Na C0 ) 2

4

2

(1)

3

© 2004 American Chemical Society In Methodologies in Asymmetric Catalysis; Malhotra, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 2004.

1

2


susceptible to replacement in an acidic medium, the removal of acetic acid is the key element in the success of this replacement reaction. This is accomplished by trapping acetic acid as it forms ^Soxhelet extractor containing sodium carbonate). Four classes of dirhodium(II) carboxamides have been synthesized, and they are illustrated in Scheme 1: MEPY = methyl 2-oxopyrrolidine-carboxylate (4), MEOX = methyl 2-oxooxazolidine-carboxylate (5), MPPIM = methyl 3phenylpropanoyl-2-oxoimidazolidine-carboxylate (d), and IBAZ = isobutyl 2oxoazetidine-carboxylate (7). These catalysts are constructed with four bridging ligands so that two nitrogens and two oxygens reside on each rhodium, and the nitrogens (or oxygens) are cis to each other. This places the carboxylate attachment in two adjacent quadrants and allows convenient access to the substrate bound to the axial site of rhodium.

O'

N

"COOMe

1/

1/

,

O

N

COOMe

1/

1/

.

Rh—Rh (2.46A)

Rh—Rh (2.46A)

Rh (5S-MEPY)

Rh (4S-MEOX)
95% ee. Similarly high enantioselectivities are obtained with allylic diazoacetamides (75), and somewhat lower selectivities are reported for homoallylic systems (75, 15). This selectivity has recently been extended to phenyldiazoacetates that are typically unreactive with dirhodium(II) carboxamidates (16). The azetidinoneligated dirhodium(II) catalysts, being more reactive towards diazo decomposition, are effective for these transformations (77). Application to the synthesis of milnacipran and some of its analogues (Scheme 6) is illustrative (18). Here, turnover numbers up to 10,000 were effective, and high enantioselectivities could be achieved. 2

4


2

N

R

2

1.0-0.01 mol% Rh (4S-MEAZ) 2

4

Ph

4

CH2CI2 >70% vH

O N

HoN

1/1/

Ph

H

COOMe

R = H, 68% ee R = Me, 94% ee

Et N 2

Rh-Rh

/|/|

Rh2(4S-MEAZ)

milnacipran (a cyclopropane - NMDA recepto r antagon ist)

R

4

Scheme 6

An extension of these catalysts for cw-selective intermolecular cyclopropanation has been achieved. We had previously observed that Rh (45IBAZ) gave the cis isomer predominantly and with high % ee (7). Subsequently, Katsuki and coworkers had developed their salen-bino ligand (Scheme 7) for exceptional selectivity in reactions ofterf-butyldiazoacetate 2

4

In Methodologies in Asymmetric Catalysis; Malhotra, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 2004.

7 with styrène (19,20). We extended our earlier work by using a chiral alkyl group on the ester attachment for the azetidinone ligand, Rh2(S,i?-MenthAZ)4, and this improved diasteroselectivity for reactions with styrene (21). Application to the synthesis of a urea-PETT analog (Scheme 8), demonstrated even higher stereoselectivity. With 2,4,6-trimethylstyrene diastereocontrol was 92:8 (cis:trans), and the cis isomer was produced in 97% ee (21).

P h

^ N CHCOOR +

2

J ^

P

h

v &

C

O

O

R

+


preferred H

w. Rh (4S-IBAZ) 2

4

R = Bu dr = 24:76 (t/c) %ee =71(0, 94(c) (21) f

R = (teHii)£H

dr= 34:66 (fcfc) %ee= 77(0,95(c) (7)

l / i /

Rh^-Rri Rh (S,fi-MenthAZ) 2

4

Co(salen-bino) RuCI(MPPIM) catalysts this process occurs with exceptional selectivity (Scheme 9) (2). With Rh2(45-MPPIM> the S-enantiomer of the γlactone product is formed, whereas with Rh(4/?-MPPIM>t the Λ-enantiomer of 4

2


8 Cl

Cl Etl/KgCO^ acetone 99%

OH

Cl

Ο

(1 ) BuLi/THF ρ (2) DMF 75%

r

Ph PMeBr, BuLi/THF 3


Cl N CHCOO Bu Rh (S,rt-MenthAZ) CH Cl2

1

f

2

boCBu

2

Q

4

2

97% ee cis:trans = 82:18 3 steps Cl Η

r

Η HIV-1 reverse transcriptase inhibitor (2^

Scheme 8 the γ-lactone product is preferentially obtained (23). Yields are good, and regioselectivity is > 20:1. This methodology has been applied to the synthesis of lignans (Scheme 10) that are readily accessible from 3-substitutedbutyrolactones (Scheme 10) (23). Applications to the total syntheses of Λbaclofen (24% deoxyxylolactone (Scheme 11) (25,26), and deoxyxylolactam (27) have been reported.


9 R'^-^O

Rh (MPPIM) CH2CI2 55-66% 2

Λ'

N

2

R-^N^Q

4

91-96%ee > 95% regiosel activity

Rh (4S-MPPIM)

4

— + ~ S-enantiomer

Rh (4fl-MPPIM)

4

— • R-enantiomer

2

2

0


Ph' Ο

Tsl

ΧΟΟΜθ

Rrf Rrf Rh (4S-MPPIM) 2

4

Scheme 9

Ο A r

/5^A H 0

Scheme 10



10

94%ee;dr=94:6

94% ee

H

OR preferred Scheme 11

In defining the preferential selectivities in the formation of deoxyxylolactone, diastereocontrol is obviously determined by the preference of the OR group (Scheme 11) for an orientation anti to the ester's ether oxygen. These same or similar control features can be seen in reactions of cyclohexyl diazoacetates where preferential equatorial C-H insertion occurs because the metal carbene unit is in the axial conformation (28). In these cases it is the face of the catalyst surface with its attached substituents that places a steric barrier on the reactive conformation of the intermediate metal carbene.


11


Another facet of these transformations is the ability of chiral substrates to distinguish match and mismatch with the chiral dirhodium(II) carboxamidate (28, 29). This feature is clearly evident in reactions of steroidal diazoacetates (for example, Scheme 12) (30). Here the 5-configured cholesterol undergoes preferential insertion into the 2-position with Λ-confïgured dirhodium(II) carboxamidates, but insertion into the 3-position to form a strained β-lactone occurs with the S-configured catalyst. Access to the 4-position is restricted.

Rh L CH2CI2 80-81% 2

4

Me Me

Rh (5f?-MEPY)

94

6

Rh2(4/?-MEOX)

4

89

11

Rh2(4S-MEOX)

4

10

90

2

4

\.,COOMe

I 0

Λ

I

Ν

Λ

Ο

Η

A/

1

Ν

COOMe

h^Rh

Λ

Rh Rh

Rh (4S-MEOX) 2

4

Rh (5f?-MEPY) Scheme 12 2

4


12

Rhodium(II) Catalysts as Chiral Lewis Acids Evidence has recently been reported of the catalytic use of chiral dirhodium(II) carboxamidates for the hetero-Diels-AIder reaction (eq 2) (31).

^

Ar


0

Μ

CH CI 2

w

2

up to 95% ΘΘ

θ

Here the major advantage of these catalysts is that they can be employed with TON of 10,000, which is a vast improvement over applications of other chiral Lewis acids to the same transformation.

Literature Cited 1. Doyle, M . P.; Ren, T. Prog. Inorg. Chem. 2001,49,113-168. 2. Doyle, M . P.; McKervey, Μ. Α.; Ye, T. Modern Catalytic Methods for Organic Synthesis with Diazo Compounds; John Wiley & Sons, Inc.: New York, NY, 1998. 3. Doyle, M . P. in Catalysis byDi-and PolynuclearMetal Cluster Complexes; Adams, R. D.; Cotton, F. Α., Eds.; VCH Publishers: New York, NY, 1998; chapter 7. 4. (a) Doyle, M . P.; Winchester, W. R.; Hoorn, J. Α. Α.; Lynch, V.; Simonsen, S. H.; Ghosh, R J. Am. Chem. Soc. 1993, 115, 9968-9978. (b) Doyle, M . P.; Winchester, W. R.; Protopopova, M . N.; Kazala, A. P.; Westrum, L. J. Org. Syn. 1996, 73, 13-24. 5. Doyle, M . P.; Dyatkin, A. B.; Protopopova, M . N.; Yang, C. I.; Miertschin, C. S.; Winchester, W. R.; Simonsen, S. H.; Lynch, V.; Ghosh, R. Recl. Trav. Chim. Pays-Bas 1995, 114, 163-170. 6. Doyle, M . P.; Zhou, Q.-L.; Raab, C. E.; Roos, G. H. P.; Simonsen, S. H.; Lynch, V. Inorg. Chem. 1996, 35, 6064-6073. 7. Doyle, M . P.; Zhou, Q.-L.; Simonsen, S. H.; Lynch, V. Synlett 1996, 697698. 8. Doyle, M . P. In Catalytic Asymmetric Synthesis, Second Edition; Ojima, I., Ed.; John Wiley & Sons, Inc.: New York, NY, 2000; chapter 5. 9. Doyle, M . P.; Forbes, D.C.;Chem. Rev. 1998, 98, 911-935. 10. Davies, H. M . L.; Antoulinakis, E. G. Org. Rxns. 2001, 57, 1-326. 11. Doyle, M . P.; Bagheri, V.; Wandless, T. J.; Harn, Ν. K.; Brinker, D. Α.; Eagle, C. T.; Loh, K.-L. J. Am .Chem. Soc. 1990, 112, 1906-1912. 12. Doyle, M . P.; Kalinin, Α. V. J. Org. Chem. 1996, 61, 2179-2184.



13 13. Doyle, M . P.; Austin, R. E.; Bailey, A . S.; Dwyer, M . P.; Dyatkin, A . B.; Kalinin, Α. V.; Kwan, M . M . Y.; Liras, S.; Oalmann, C. J.; Pieters, R. J.; Protopopova, M . N.; Raab, C. E.; Roos, G. H. P.; Zhou, Q.-L.; Martin, S. F. J. Am. Chem. Soc. 1995, 117, 5763-5775. 14. Doyle, M . P.; Peterson, C. S.; Zhou, Q.-L.; Nishiyama, H . J. Chem. Soc., Chem. Commun. 1997, 211-212. 15. Doyle, M . P.; Kalinin, Α. V. J. Org. Chem. 1996, 61, 2179-2184. 16. Doyle, M . P.; Zhou, Q.-L.; Charnsangavej, C.; Longoria, Μ. Α.; McKervey, Μ. Α.; Garcia, C. F. Tetrahedron Lett. 1996, 37, 4129-4132. 17. Doyle, M . P.; Davies, S. B.; Hu, W. Org. Lett. 2000, 2, 1145-1147. 18. Doyle, M . P.; Hu, W. Adv. Synth. & Catal. 2001, 343, 299-302. 19. Niimi, T.; Uchida, T.; Irie, R.; Katsuki, T. Tetrahedron Lett. 2000, 41, 3647-3651. 20. Uchida, T.; Irie, R.; Katsuki, T. Tetrahedron 2000, 56, 3501-3509. 21. Hu, W.; Timmons, D. J.; Doyle, M. P. Org. Lett. 2002, 4, 901-904. 22. Högberg, M . ; Sahlberg, C.; Engelhardt, P.; Noréen, R.; Kangasmetsä, J.; Johansson, N. G.; Oberg, B.; Vrang, L.; Zhang, H.; Salhberg, B. L.; Unge, T.; Lövgren, S.; Fridborg, Κ.; Bäckbro, Κ. J. Med. Chem. 1999, 42, 4150. 23. Bode, J. W.; Doyle, M P.; Protopopova, M . N.; Zhou, Q.-L. J. Org. Chem. 1996, 61, 9146-9155. 24. Doyle, M . P.; Hu, W. Chirality 2002, 14, 169-172. 25. Doyle, M . P.; Dyatkin, A. B.; Roos, G. H. P.; Cañas, F.; Pierson, D. Α.; van Basten, Α.; Müller, P.; Polleux, P. J. Am. Chem. Soc. 1994, 116, 4507-4508. 26. Doyle, M . P.; Tedrow, J. S.; Dyatkin, A . B.; Spaans, C. J.; Ene, D. G. J. Org. Chem. 1999, 64, 8907-8915. 27. Doyle, M . P.; Phillips, I. M . ; Timmons, D. J. Adv. Synth. & Catal. 2002, 344, 91-95. 28. Doyle, M . P.; Kalinin, Α. V.; Ene, D. G. J. Am. Chem. Soc. 1996, 118, 8837-8846. 29. Doyle, M . P.; Kalinin, Α. V. Tetrahedron Lett. 1996, 37, 1371-1374. 30. Doyle, M . P.; Davies, S. B.; May, E. J. J. Org. Chem. 2001, 66, 8112-8119. 31. Doyle, M . P.; Phillips, I. M . ; Hu, W. J. Am. Chem. Soc. 2001, 123, 53665367.


Methodologies in Asymmetric Catalysis - American Chemical Society

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