ENANTIOSELECTIVE INTRAMOLECULAR CYCLOPROPANATIONS OF ALLYLIC AND HOMOALLYLIC DIAZOACETATES AND DIAZOACETAMIDES USING CHIRAL DIRHODIUM(II) CARBOXAMIDE CATALYSTS

Citation
Mp. Doyle et al., ENANTIOSELECTIVE INTRAMOLECULAR CYCLOPROPANATIONS OF ALLYLIC AND HOMOALLYLIC DIAZOACETATES AND DIAZOACETAMIDES USING CHIRAL DIRHODIUM(II) CARBOXAMIDE CATALYSTS, Journal of the American Chemical Society, 117(21), 1995, pp. 5763-5775
Citations number
111
Categorie Soggetti
Chemistry
ISSN journal
00027863
Volume
117
Issue
21
Year of publication
1995
Pages
5763 - 5775
Database
ISI
SICI code
0002-7863(1995)117:21<5763:EICOAA>2.0.ZU;2-I
Abstract
Diazo decomposition of allylic and homoallylic diazoacetates 10a-p and 22a-j catalyzed by chiral dirhodium(II) tetrakis[methyl 2-pyrrolidone -5(S)-carboxylate], Rh-2(5S-MEPY)(4) (7), and its enantiomer, Rh-2(5R- MEPY)(4) (8), produces the corresponding intramolecular cyclopropanati on products 11a-p and 23a-j in good to excellent yields and with excep tional enantioselectivity. Higher enantiocontrol is observed with ally lic diazoacetates than with their homoallylic counterparts, but allyli c diazoacetates are subject to greater variations in enantioselectivit ies with changes in substitution patterns on the carbon-carbon double bond. For example, the enantioselectivities in the intramolecular cycl opropanations of 3-alkyl/aryl-2(Z)-alken-1-yl diazoacetates are genera lly greater than or equal to 94%, whereas the cyclizations of the homo logous 4-alkyl/aryl-3(Z)-alken-1-yl diazoacetates are typically in the range of 70-90% ee. The corresponding 3-alkyl/aryl-2(E)-alken-1-yl an d 4-alkyl/aryl-3(E)-alken-1-yl diazoacetates undergo cyclization with slightly lower ee's (54-85%). Although the Rh-2(5S-MEPY)(4)-catalyzed cyclization of the 2-methallyl diazoacetate 10c proceeds with only 7% ee, alternative chiral dirhodium(II) catalysts, including those with m ethyl N-acylimidazolidin-2-one-4(S)-carboxylate ligands such as Rh-2(4 S-MACIM)(4) (14) and Rh-2(4S-MPAIM)(4) (15), may be employed to increa se the level of enantiocontrol to 78 and 65%, respectively. Some allyl ic diazoacetamides also undergo highly enantioselective cyclization to form cyclopropyl lactams as illustrated by the diazo decomposition of N-allyl diazoacetamide (19) in the presence of dirhodium(II) tetrakis [methyl 2-oxazolidinone-4(S)-carboxylate], Rh-2(4S-MEOX)(4), to give t he 3-azabicydo[3.1.0]hexan-2-one 20 in 98% ee. The absolute configurat ion and the level of enantiocontrol in these intramolecular cyclopropa nations have been interpreted by a transition state model in which the important determinants are (i) the preferred conformation about the r hodium-carbon bond; (ii) the trajectory of approach of the double bond to the metallocarbene center; and (iii) the orientation of the double bond with respect to the chiral face of the catalyst.