J. Org. Chem. 1992,57,5031-5034 sublimed at room temperature into the hot zone, concurrent with Cs, which waa held at a temperature of ca. 100-110 "C. Argon flow waa controlled by a needle valve (0.2 mmol/min). The mixture depoeited onto a CsI window held at 28 K. The matrim were a transparent, deep-sea blue. &action of Compound 3 with CBin the Gas P h a ~ Ob: servation of 1 by FTIB in an Argon Matrix. This reaction was carried out in easexitially the same manner 88 with 4, the main difference being that the dibromo compound 3 waa mixed with the argon in a 500:l ratio prior to deposition. Computations. Ab initio SCF calculations were carried out on IBM Rs6oo0/540and 6OOO 550 computers using the GAUSSIAN 88 and GAUSSUN 90 program.b'U Calculation of the IR frequencies were done at the restricted Hatree-Fock level on optimized geometries, using a 631G*basis set. The standard 0.9 multiplicative correction factor waa used.
B
Acknowledgment. This work was supported by the National Science Foundation (DMR 8807701). The M'IR spectrometer was purchmd with support from NSF grant CHE 9121643 and the computer with support from NSF grant CHE 9022151. We are grateful to Dr. V. Balaji for assistance with the calculations.
we encountered an intriguing reaction providing products in which an unusual migration of the ester moiety6 had occurred following the regiaepecific addition of the cuprate to C-3 of 2,3-epoxy alcohol pivaloylates. Further investigation of thie unexpected result has shown that this reaction is synthetically useful and provides a convenient protocol for the direct, regioselective preparation of an important class of monoprotected 1,a-diols that are only difficulty accessed by more traditional means. At the outaet of our investigations trans-3-propyloxiranemethanoltrimethylacetate (1) was added to a solution of Bu&uLi/TMSOTf (2.41.2 equiv relative to 1) in &O at -78 OC. After stirring for 30 min at -78 OC and then a t room temperature for 30 min, the reaction was quenched with aqueous NH4C1/NH40H(101). Utilizing this protocol le was isolated as the major product, with the ester moiety residing on the secondary carbon. The transesterification was shown to be under thermodynamic control as the "unrearranged" addition product (If) predominated when the reaction was quenched at -78 OC (eq 1). 2 4 equw
ppr*;\
(18)GAUSSIAN 88. Frisch, M. J.; Head-Gordon, M.; Schlegel, H. B.; Raghavachari, S.; Binkley, J. S.; Gonzalez, C.; Defrees, D. J.; Fox, D. J.; Whiteside, R. A.; Seeger, R.; Melius, C. F.; Baker, J.; Martin, R.; Kahn, L. R,Stewart, J. J. P.; Fluder, E.M.; Topiol, S.; Pople, J. A. GAUSSZAN, G a w i a n Inc., Pittsburgh, PA, 1988. (19)GAUSSIAN 90. Frisch, M. J.; Head-Gordon, M.; Trucks, G. W.; Foreaman, J. B.; Schlegel, H. B.; Raghavachari, S.; Robb, M. A.; Binkley, J. S.; Gonzalez, C.; Defreea, D. J.; Fox, D. J.; Whitaide, R. A.; Seeger, R.; Melius, C. F.; Baker, J.; Martii, R.; Kahn, L. EL; Stewart, J. J. P.; Topiol, S.; Pople, J. A. GAUSSIAN, Gaussian Inc., Pittsburgh, PA, 1990.
Trimethyleilyl Trifluoromethaneeulfonate Mediated Dfalkylcuprate Addition to Epoxy Esters: An Unusual Intramolecular Transeeterification Process Gary A. Molander*J and Kevin L. Bobbitt2 Department of Chemistry and Biochemistry, University of Colorado at Boulder, Boulder, Colorado 80309-0215 Received May 19, 1992
Epoxides are important starting materials and intermediatea in organic synthesis because of their ready aweas and their high reactivity toward nucleophiles. The emergence of the Sharpless epoxidation procedure has increased the importance of these electrophiles by providing a route to 2,3-epoxy alcohols of high enantiomeric purity? Development of synthetic methods allowing regioselective ring opening of 2,3-epoxy alcohols by a wide range of nucleophiles further enhances the utility of epoxides in organic synthesis.' While investigating the regiochemistry of Lewis acid promoted organocuprate addition to trimethylacetate-protected 2,3-epoxy alcohols,5 (1)Alfred P.Sloan Foundation Fellow, 1987-1991. (2)National Inetituta of Health Postdoctoral Fellow, 1991-1993. (3) (a) Caron, M.; Sharpless, K. B. J. Org.Chem. 1986,50,1560.(b) Chong, J. M.; Sharpleas,K. B. J. Org.Chem. 1985,50,1563.(c) Kabuki, T.; Sharpless, K. B. J. Am. Chem. SOC.1980, 102, 5974. (d) Gao, Y.; Klunder, J. M.; H a " , R. M.; Maeamune, H.; KO,S. Y.;Sharpless, K. B. J. Am. Chem. SOC.1987,109,5765.(e) Roseiter, B. E. In Asymmetric Synthesis; Morrieon, J. S., Ed.; Academic Prese: New York, 1985; Vol 5. (4)Hanson, R. M. Chem. Rev. 1991,91,437-475.
so3 1
I Bu
)L0
1
-
1 2 equw TMSOTf EI20. -78'C
room temp. quench: -78'C quench:
O K , Bu
aPr.
rcoK'B"
n-PI,
0
RBU~CUL~
+
OH
(0
n - B u h OH
0
73%
If. c5%
UndEtecled (4%)
72%
1 :.
The selectivity for acylation of the secondary alcohol in preference to the primary alcohol is reminiscent of the dibutyltin-promoted monoacylation of l,%diols reported previously by Roelens and ~o-workers.~However,.given the uncertainty of the role that the trialkylsilyl trfflates play in the present reaction? a mechanistic rationale for the observations reported is difficult. It would seem reasonable that the usual intramolecular acyl migration through a dioxolanyl intermediate is operational in these transformations.@ Thus, the primary alkoxide generated in this equilibrium process could be preferentially trapped by an electrophile (R,SiOTf), shutting down the intramolecular acyl migration and leaving the carboxylate at the secondary alcohol center. However, all efforts to trap silyl ether products have failed, even in those instances where t-BuMe&OTf was utilized as the electrophile under conditions where these protected alcohols were stable.1° Consequently, no evidence exists to document such a proposed mechanism. (5)For tome examplea of organocuprateadditions to epoxides, see: (a) Lipshutz, B. H.; Kozlowski, J.; Wilhelm, R. 5.J. Am. Chem. SOC.1982, A.; Jachiet, D.; Normant, J. F. Tetrahedron 1986, 104,2305.(b) Ale&, 42,5607. (c) Lipshutz, B. H.; Wilhelm, R. S.; Kozloweki, J. A.; Parker, D. J. Org. Chem. 1984,49,3928.(d) Kurth, M. J.; Abreo, M. A. Tetrahedron Lett. 1987,28,5631.(e) Kurth, M. J.; Abreo, M. A. Tetrahedron 1990,46,5085.(f) Lipshutz, B. H.; Sengupta, S. Org. React. 1992,41,135. (6)(a) Hatch, G. B.; Adkine, H. J. Am. Chem. SOC.1937,59,1694.(b) Sugihara, J. M.Adu. Carbohydr. Chem. Biochem. 1953,8,1.(c) Lemieux, R. U. In Molecular Reamngemente; deMayo, P., Ed.; Interscience: New York, 1964;Vol. 2. (d) Acheson, R. M. Acc. Chem. Res. 1971,4, 177. (7)Ricci, A.; Roelens, S.; Vannucchi A. J. Chem. SOC.,Chem. Commun. 1985, 1457. (8)(a) Lipshutz, B. H.; Ellsworth, E. L.; Siahaan, T. J.; Shirazi, A. Tetrahedron Lett. 1988,29,6677.(b) Lipshutz, B. H.; Ellsworth, E. L.; Dimock, S.H.; Smith, R. A. 9. J . Am. Chem. SOC.1990,112,4404and references cited therein. (9) McClellend, R. A.; Seaman, N. E.; Cra", D. J. Am. Chem. SOC. 1984,106,4511. (10)For example, the reaction of 1 with Me2CuLi/t-BuMe&OTf provides 57% of la and 0.6).2-4 The N-alkylides (2, R3 = alky!) were converted into 5 and toluenes (6), and both compounds were produced via radical-forming and -destroying pathways from 6-(l-aminoalkyl)-5-methylene-1,3-cyclohexadienes(3), which were initially formed by a [2,3] sigmatropic rearrangement of 2.5 The conversion of 3 to 4 requires a [1,3] antarafacial migration of a hydrogen a t the 6-position of 3 to the exo-methylene carbon (C-8) under thermal condition.
.%--:-ANMe2
.y R3
When R3of 3 is an alkyl group, its steric bulk interferes with the torsion of the molecule, thus allowing the [1,3] proton migration. Therefore, the carbon-carbon bond between C-6 and C-7 may be cleaved homolytically to a radical pair, radical recombination gives 5, and hydrogen atom abstraction produces 6.' Addition of a strongly basic amine to the reaction could aid the conversion of 3 to 4 by a proton-dissociation and -recombination pathway. Irradiation by W light could assist the isomerization from 3 to 5 via the radical pathway or a suprafacial [1,3] migration of the aminoalkyl group to the C-8 carbon.6 (1) (a) Pine, S. H. Org. React. (N.Y.) 1970,18,403. (b) Lepley, A. R.; Giumanini, A. G. In Mechanism of Molecular Migrations; Thyagarajan, B. S., Ed.; Wiley-Interscience: New York, 1971; Vol. 3, p 297. (c) ZugrHvescu, I.; Petrovanu, M. N- Ylid Chemistry; McGraw-Hill: New York, 1976. (2) Nakano, M.; Sato, Y. J. Org. Chem. 1987,52,1844. (3) Shirai, N.; Sato, Y. J. Org. Chem. 1988,53, 194. ( 4 ) Shirai, N.; Watanabe, Y.; Sato, Y. J. Org. Chem. 1990,55, 2767. ( 5 ) Okazaki, S.; Shirai, N.; Sato, Y. J. Org. Chem. 1990.55, 334.
0022-3263/92/ 1957-5034$03.00/0 0 1992 American Chemical Society
