Allenes 169 and alkynes 170 are prepared by hydrogenolysis of propargyl compounds with several hydrides. Triethylammonium formate is used most conveniently under mild conditions [45]. Chromium tricarbonyl-complexed phenylallene172 was prepared from the carbonate 171[46]. The alkyne174 was obtained selectively from the propargyl formate173having an amino group [47].
169
THF, 79%
171 172
Pd(acac)2, P(n-Bu)3 + HCO2NH4
+
C6H13
C6H13
OCHO
HN
HN Boc
Boc Pd(0)
OCO2Me
Cr(CO)3 Cr(CO)3
acetylene / allene = 97 / 3 Pd(acac)2, P(n-Bu)3
THF, 25 °C, 93%
R2 R1
X
R2 R1
H H R2 H
R1
168 170
+
173 174
Et3N HCO2H
Reaction of propargyl formate175affords two products179and181depending on the kind of intermediates being subjected to hydrogenolysis with formate. When 5-exo cyclization of176and 3-exo cyclization of177to give the cyclopropane178 occurred before the hydrogenolysis, the bicyclo[3.1.0]hexane 179 was obtained.
On the other hand, the cyclopentane 181 was formed by hydrogenolysis of 176, and the cyclopentane 181was obtained by Pd-catalyzed cyclization of180 [3].
179 E
E OCHO
E
E Pd-H
E E E E E
Pd-H
HPd E E
E E
E MeCN, 85 °C
181 54%
1 : 3
175 176
Pd(OAc)2, PPh3
177 178
180
179 : 181
Pd-catalyzed reduction of propargyl compounds with SmI2 is possible in the presence of proton sources [48]. Yoshida and Mikami reported a dramatic change of chemoselectivity in the reduction of propargyl phosphates with SmI2 and var- ious proton sources [49]. The alkyne 183 was a main product from the primary propargyl phosphate 182 using t-BuOH as a proton source. The allene 184 was a minor product. The propargyl phosphate 185 bearing an ester group gave the allene186 exclusively. The chemoselectivity of the reduction of secondary phos- phate 187 depends on the proton sources. The allene 188 was obtained by the use oft-BuOH, and the alkyne 189was a major product when dimethylL-tartrate was used.
t-BuOH, 80% > 99 186
dimethyl L-tartrate, 81%
94 : 6 +
< 1 THF, rt, 50%
+ 185
C8H17
H C8H17
OPO(OEt)2
C8H17 Me
MeO2C
H MeO2C OPO(OEt)2
Ph Ph
OPO(OEt)2
Et Ph Et
187
183 184 + Pd(PPh3)4, t-BuOH
THF, rt, 83%
+ Pd(PPh3)4, THF proton source, rt
85 15
Pd(PPh3)4, t-BuOH 182
+
> 99%
188 189
SmI2
SmI2
SmI2
Et
Furthermore Mikami and Yoshida have studied regio- and enantioselective syn- thesis of allenic esters by Sm(II)-mediated reduction of propargyl compounds.
Attempted chirality transfer by SmI2reduction of the optically active propargylic phosphate190 (91 % ee) provided the racemic compound191. Then they carried out dynamic kinetic resolution based on asymmetric protonation using racemic propargyl phosphate192. Among several chiral proton sources, (R)-pantolactone 193 gave the optically active allenic ester 194 with the highest % ee (95 % ee).
Interestingly the yield of194was 68 %, which is higher than the maximum yield (50 %) obtained by ordinary kinetic resolution. The efficient asymmetric proto- nation is attained due to the chelation of the chiral alcohol 193 with Sm (III) intermediate species possessing high Lewis acidity and oxophilicity [50].
191
192
(R)-193
(R)-194 68%, 95% ee
racemic
+ SmI2
Pd(PPh3)4,t-BuOH THF, 10 min, 53%
91% ee
+ SmI2
Pd(PPh3)4, 190
CO2Me
CO2Me OPO(OEt)2
CO2Me OPO(OEt)2
CO2Me O
O OH
When propargyl carbonates195 are treated with a Pd catalyst in the absence of other reactants, β-H elimination from the propargylpalladium intermediates 196 occurs to give conjugated enynes 197. Formation of cumulative 1,2,3-alkatrienes 199 from the allenylpalladiums 198 does not take place. Preparation of the con- jugated ene–yne–ene system201in high yield from the propargyl carbonate 200 is an example [51].
201 E/Z = 57/43
197
199
Pd(0) 196
195
200
198 Pd(OAc)2, PPh3 THF, reflux, 96%
MeO2CO
R1 H
R1
PdOMe R2 R1
MeOPd
R1
H R2 R1
H
R2 R2
R2
C6H13
OCO2Me
C6H13
C6H13
C6H13
• • •
References
1. Reviews: (a) J. Tsuji,Angew. Chem. Int. Ed. Engl.,34, 2589 (1995); (b) J. Tsuji and T. Mandai, in Metal-Catalyzed Cross-Coupling Reactions, Eds. F. Diedrich and P. J.
Stang, Wiley-VCH, New York, 1998, p. 455.
2. R. Grigg, R. Rasul, J. Redpath, and D. Wilson,Tetrahedron Lett.,37, 4609 (1996).
3. A. G. Steinig and A. de Meijere,Eur. J. Org. Chem., 1333 (1999).
4. J. Bohmer, R. Grigg, and J. D. Marchbank,Chem. Commun., 768 (2002).
5. W. Oppolzer, A. Pimm, B. Stammen, and W. E. Hume, Helv. Chim. Acta, 80, 623 (1997).
6. R. Grigg, R. Rasul, and V. Savic,Tetrahedron Lett.,38, 1825 (1997).
7. N. Monteiro, A. Arnold, and G. Balme,Synlett, 1111 (1998).
8. S. Cacchi, G. Fabrizi, and L. Moro,Tetrahedron Lett.,39, 5101 (1998).
9. S. Ogoshi, S. Nishiguchi, K. Tsutsumi, and H. Kurosawa, J. Org. Chem., 60, 4650 (1995).
10. Review, J. Tsuji, and T. Mandai,J. Organomet. Chem.,451, 15 (1993).
11. J. Tsuji, T. Sugiura, and I. Minami,Tetrahedron Lett.,27, 731 (1986).
12. Y. Imada and A. Alper,J. Org. Chem.,61, 6766 (1996).
13. M. Ishikura, H. Uchiyama, and N. Matsuzaki,Heterocycles,55, 1063 (2001).
14. J. A. Marshall, M. A. Wolf, and E. M. Wallace,J. Org. Chem.,62, 367 (1997).
15. G. S. Bartley, and E. M. Wallace,J. Org. Chem.,61, 5729 (1996);J. Org. Chem.,60, 796 (1995); J. A. Marshall and E. A. Van Devender, J. Org. Chem.,66, 8037 (2001).
16. W. Y. Yu and H. Alper,J. Org. Chem.,62, 5684 (1997).
17. W. J. Xiao and H. Alper,J. Org. Chem.,62, 3422 (1997).
18. A. Ogawa, H. Kuniyasu, N. Sonoda, and T. Hirao,J. Org. Chem.,62, 8361 (1997).
19. T. Mandai, Y. Tsujiguchi, S. Matsuoka, J. Tsuji, and S. Saito, Tetrahedron Lett.,35, 5697 (1994).
20. J. Kiji, T. Okano, E. Fujii, and J. Tsuji,Synthesis, 869 (1997).
21. (a) J. Tsuji and T. Nogi, Tetrahedron Lett., 1801 (1966); (b) T. Nogi and J. Tsuji, Tetrahedron,25, 4099 (1969).
22. J. Kiji, T. Okano, H. Kitamura, Y. Yokoyama, S. Kubota, and Y. Kurita,Bull. Chem.
Soc. Jpn.,68, 616 (1995).
23. S. Ma and A. Zhang,J. Org. Chem.,67, 2287 (2002).
24. T. Konno, M. Tanikawa, T. Ishihara, and H. Yamanaka,Chem. Lett., 1360 (2000).
25. S. Miniere and J. C. Cintrat,J. Org. Chem.,66, 7385 (2001).
26. Y. Tsuji, M. Taniguchi, T. Yasuda, T. Kawamura, and Y. Obora,Org. Lett., 2, 2635 (2000).
27. M. Suginome, A. Matsumoto, and Y. Ito,J. Org. Chem.,61, 4884 (1996).
28. Y. Tamaru, S. Goto, A. Tanaka, M. Shimizu, and M. Kimura,Angew. Chem. Int. Ed.
Engl.,35, 878 (1996).
29. Review: J. A. Marshall,Chem. Rev.,100, 3174 (2000).
30. (a) J. A. Marshall and N. D. Adams,J. Org. Chem.67, 733 (2002); (b) J. A. Marshall and G. M. Schaaf,J. Org. Chem.,66, 7825 (2001).
31. J. M. Aurrecoechea, M. Arrate, and B. Lopez,Synlett, 872 (2001).
32. J. A. Marshall and C. M. Grant,J. Org. Chem.,64, 696 (1999).
33. J. A. Marshall, H. R. Chobanian, and M. M. Yanik,Org. Lett.,3, 3369 (2001).
34. H. Ohno, H. Hamaguchi, and T. Tanaka,Org. Lett.,2, 2161 (2000).
35. T. Mandai, T. Nakata, H. Murayama, H. Yamaoki, M. Ogawa, M. Kawada, and J. Tsuji,Tetrahedron Lett.,31, 7179 (1990).
36. S. Condon-Gueugnot and G. Linstrumelle,Tetrahedron Lett. 34, 3853 (1993);Tetra- hedron,56, 1851 (2000).
37. J. Tsuji, H. Watanabe, I. Minami, and I. Shimizu,J. Am. Chem. Soc.,107, 2196 (1985).
38. P. Wipf and M. J. Soth,Org. Lett.,4, 1787 (2002).
39. C. Foumier-Nguefack, P. Lhoste, and D. Sinou,Synlett, 553 (1996).
40. M. Yoshida, M. Fujita, T. Ishii, and M. Ihara,J. Am. Chem. Soc.,125, 4874 (2003).
41. (a) J. R. Labrosse, P. Lhoste, and D. Sinou,Org. Lett.,2, 527 (2000); (b) J. R. Lab- rosse, P. Lhoste, and D. Sinou,J. Org. Chem.,66, 6634 (2001).
42. J. A. Marshall and M. A. Wolf,J. Org. Chem.,61, 3238 (1996).
43. Y. Kozawa and M. Mori,Tetrahedron Lett.,42, 4869 (2001).
44. Y. Kozawa and M. Mori,Tetrahedron Lett.,43, 1499 (2002).
45. Review, J. Tsuji, T. Sugiura, and I. Minami,Synthesis, 1 (1996).
46. M. Ansorge, K. Polborn, and T. J. J. M¨uller,J. Organomet. Chem.,630, 198 (2001).
47. T. Mandai, T. Matsumoto, M. Kawada, and J. Tsuji, Tetrahedron Lett., 34, 2161 (1993).
48. J. Inanaga, Y. Sugimoto, and T. Hanamoto,Tetrahedron Lett.,33, 7035 (1992).
49. A. Yoshida and K. Mikami,Synlett, 1375 (1997).
50. K. Mikami and A. Yoshida,Angew. Chem. Int. Ed. Engl.,36, 858 (1997);Tetrahedron, 57, 889 (2001).
51. T. Mandai, Y. Tsujiguchi, S. Matsuoka, and J. Tsuji, Tetrahedron Lett., 34, 7615 (1993).
Pd(0)- and Pd(II)-Catalyzed Reactions of Alkynes and Benzynes