3022
J. Org. Chem. 1985,50, 3022-3024
@-anisyl)-3-hydroxy-2-methyl-4-hexenoyl]pyrrolidine, 97060-64-5; In this communication, we report a parallel investigation syn-N- [5-(p-anisyl)-2,3-dimethyl-5-oxopentanoyl]pyrrolidine, of the stereochemistry of the reaction of the Z and E 97060-65-6;anti-N-[5-(p-anisyl)-2,3-dimethyl-5-oxopentanoyl]- lithium enolates of tert-butyl propionate (1 and 2, repyrrolidine, 97060-66-7;3-[ l-(p-anisyl)-l-hydroxy-2-butenyl]-N- spectively).2 The results obtained in this study clearly methylpyrrolidone, 97060-67-8; syn-3-[4-(p-anisyl)-4-0~0-2-b~-show that there is a correlation between enolate geometry tyll-N-methylpyrrolidone,97060-68-9; anti-3-[4-(p-anisyl)-4and Michael adduct stereostructure, provide additional oxo-2-butyl] -N-methylpyrrolidone,97060-69-0; N-(3-tert-butylevidence in favor of the open transition state hypothesis, 3-hydroxy-2-methyl-4-heptenoyl)pyrrolidine, 97060-70-3; synand establish a synthetically useful, stereoselective synN-(3-ethyl-5-oxc-2,6,6-trimethylheptanoyl)pyrrolidine, 97060-71-4; anti-N-(3-ethyl-5-oxo-2,6,6-trimethylheptanoyl)pyrrolidine, thesis of &keto acids having two stereocenters.
97060-72-5; 3-(6,6-dimethyl-5-hydroxy-3-hepten-5-yl)-NThe E enolate 2 was prepared in the normal mannerP3 methylpyrrolidone, 97060-73-6; syn-3-(6,6-dimethyl-5-oxo-3- by addition of tert-butyl propionate to a THF solution of hepty1)-N-methylpyrrolidone, 97060-74-7; anti-3-(6,6-dimethyllithium diisopropylamide (LDA) at -78 "C. For prepara5-oxo-3-heptyl)-N-methylpyrrolidone, 97060-75-8;N-(3-tert-bution of Z enolate 1, the method of Ireland, wherein a 23% tyl-2,6-dimethyl-3-hydroxy-4-heptenoyl)pyrrolidine, 97060-76-9; (volume/volume) mixture of hexamethylphosphoric trisyn-N-(5-oxo-3-isopropyl-2,6,6-trimethylheptanoy1)pyrrolidine, 97060-77-0; anti-N-(5-0~0-3-isopropyl-2,6,6-trimethyl- amide (HMPT) and T H F is used as solvent, was emp10yed.~ The enolate E / Z ratio was determined by heptanoyl)pyrrolidine, 97060-78-1; 3-(5-hydroxy-2,6,6-triwithdrawing an aliquot, which was treated with tert-bumethyl-3-hepten-5-yl)-N-methylpyrrolidone, 97060-79-2; syntyldimethylsilyl chloride. The resulting silyl ketene acetal 3-(5-oxo-2,6,6-trimethyl-3-hepty1)-N-methylpy~olidone, 9706080-5;anti-3-(5oxc-2,6,6-trimethyl-3-heptyl)-N-methylpyrrolidone, was analyzed by capillary GLPC. The enones investigated 97060-81-6;N-(3-tert-butyl-3-hydroxy-2,6,6-trimethyl-4-hepten- were compounds 3-6. Michael reactions were normally oyl)pyrrolidine,97060-82-7;syn-N-(3-tert-butyl-5-0~0-2,6,6-trimethylheptanoyl)pyrrolidine, 97071-46-0; anti-N-(3-tert-butylY-BuOq &R 5-oxo-2,6,6-trimethylheptanoyl)pyrrolidine, 97071-47-1; 345hydroxy-2,2,6,6-tetramethyl-3-hepten-5-yl)-N-methylpyrrolidone, I 2 3 R=Me 4 R i E I 97060-83-8; 3-(5-0~0-2,2,6,6-tetramethy1-3-heptyl)-N-methyl6 R = I-Bu 6 RzPh pyrrolidone, 97060-84-9;N-(3-tert-butyl-3-hydroxy-2-methyl-5phenyl-4-pentenoyl)pyrrolidine,97060-85-0; syn-N-(5-oxo-3phenyl-2,6,6-trimethylheptanoyl)pyrrolidine,97060-86-1; anticarried out by adding the enone to a solution of the enolate N-(5-oxo-3-phenyl-2,6,6-trimethylhept~oyl)p~rolidine, 97060a t -78 "C; reaction was either quenched after 15 min at 87-2; 3-(4,4-dimethyl-3-hydroxy-l-phenyl-l-penten-3-yl)-Nthis temperature or after the reaction mixture had been methylpyrrolidone, 97060-88-3; syn-3-(4,4-dimethyl-3-oxo-l- warmed to 25 "C for 90 min (eq 1). Diastereomer ratios phenylpentyl)-N-methylpyrrolidone, 97060-89-4;anti-3-(4,4-dimethyl-3-oxo-l-phenylpentyl)-N-methylpyrrolidone, 97060-90-7. IPBUO
Supplementary Material Available: A full description of the pethods used to assign stereostructures to the 1,4 addition products reported in Table I and a listing of the 13C NMFt chemical shifts of these products (5 pages). Ordering information is given on any current masthead page. Clayton H. Heathcock,* Mark A. Henderson David A. Oare, Mark A. Sanner Department of Chemistry University of California Berkeley, California 94720 Received April 9, 1985
Stereoselection in the Michael Addition Reaction. 3. Relationship between Ester Enolate Geometry and Adduct Stereochemistry in the Kinetic Michael Reactign of Lithium Enolates with Enones' Summary: A systematic study of the stereochemistry of the kinetic Michael addition of the Z and E lithium enolates of tert-butyl propionate has provided conclusive evidence that the stereostructure of a lithium enolate determines the stereostructure of the resulting Michael adduct. Sir: In the previous paper in this series we reported an investigation of the kinetic Michael reaction of amide lithium enolates with enones and rationalized the observed diastereoselectivity in terms of an open transition state.' (1) Part 31 in the series "Acyclic Stereoselection". For part 30, see: Heathcock, C.H.; Henderson, M. A.; Oare, D. A.; Sanner, M. A. J. Org. Chem., previous communication in this issue.
3-6
1.2
syn-1.4
-
anti I .4
were determined by 13C NMR spectroscopy or capillary GLPC. The products were identified by conversion to keto acids of previously determined ~tereostructure.',~Results are summarized in Table I. Examination of Table I reveals several interesting features. First, as we found in the reactions of amide enolates with enones,' the 1,2/1,4 ratio depends on the steric demand of the group a t the @-positionof the enone (R in 3-6). With enones 3 and 4, only the 1,4 adduct is seen, even a t -78 "C. With enone 6, mixtures of 1,2 and 1,4 gdducts are observed, E enolate 2 showing a greater propensity for 1,2 addition. With enone 5 and Z enolate 1, no reaction is observed at -78 "C; the same enone reacts with E enolate 2 a t -78 "C to give only the 1,2 adduct. Both with enones 5 and 6, reaction for 90 min at 25 "C results in 1,2 to 1,4 equilibration. Relative to the reactions of enones 3-6 with amide enolates,l the following generalizations may be made. First, the ester enolates generally show a greater intrinsic preference for 1,4 addition than do the amide enolates at -78 "C. Second, 1,2 addition is more freely reversible with the ester enolates than with the amide enolates. Third, with both types of enolates, E enolates show a greater preference for 1,2 addition than 2 enolates.6 Fourth, isolated yields of 1,4 adducts are (2) The stereochemical descriptors E and 2 are employed in the manner recommended by Evans: Evans, D. A. In "Asymmetric Synthesis"; Morrison, J. D., Ed.; Academic Press: New York, 1984; Val. 3, p 11. (3) See inter alia: Heathcock, C. H.; Buse, C. T.; Kleschick, W. A.; Pirrung, M. C.; Sohn, J. E.; Lampe, J. J. Org. Chem. 1980, 45, 1066. (4) Ireland, R. E.; Mueller, R. H.; Willard, A. K. J . Am. Chem. SOC. 1976, 98, 2868. (5) Heathcock, C. H.; Norman, M. H.; Uehling, D. E. J . Am. Chem. SOC.1985, 107,2797.
0022-3263/85/1950-3022$01.50/00 1985 American Chemical Society
J. Org. Chem., Vol. 50, No. 16, 1985 3023
Communications
Table I. Stereochemistry of Addition of Enolates 1 and 2 to Enones (Eq 1)" entry
enone
enolate
1 2 3 4 5 6 7 8 9 10 11 12
3 3 4 4
2 1 2
EIZ
ratiob
1
12:88 94:6
1
5 5
1 2 2 1 1 2 2
5 5
6 6 6 6
11:89 11:89 95:5 95:5
temp,
"C
time, min
yield, %
1,2/1,4 ratio
syn/ anti (1,4 adduct)
-78 -78 -78 -78 -78 25 -78 25 -78 25 -78 25
15 15 15 15 15 90 15 90 15 90 15 90
73
