Organometallics 1983, 2, 1625-1629
1625
Stereochemistry and Mechanism of Nucleophilic Attack by Dialkylamines on (r-Allyl)palladium Complexes Jan-E. Backvall, Ruth E. Nordberg, Krister Zetterberg, and Bjorn Akermark Department of Organic Chemistry, Royal Institute of Technology, S-100 44 Stockholm, Sweden Received March 9, 1983
Nucleophilic attack by dialkylamines on the (a-al1yl)palladium complex 1, bis[(4-methoxy-l-3-$cyclohexeny1)palladiumchloride], in the presence of triphenylphosphine takes place exclusively with trans (2) (with Me2") or stereochemistry (>98% trans) to give cis-3-(dimethylamino)-6-methoxycyclohexene cis-3-(diethylamino)-6-methoxycyclohexene (3) (with Et2"). In the presence of AgBF, and triphenyl(4) and 3-(diethylphosphine two additional products, trans-3-(diethylamino)-6-methoxycyclohexene amino)-4-methoxycyclohexene(5), are formed (4 up to 14% relative to 3). Carbonylation of 1 in the presence of diethylamine gave the amide 6 regiospecifically, suggesting that a (a-ally1)palladiumcomplex is involved. NMR experiments suggest the formation of a a-allyl complex on addition of phosphine ligands to 1. The introduction of an amine in the allylic position of an alkene is an important transformation in organic synthesis. So far there are no direct procedures known for this transformation, but methods leading to allylic amides have been reported.'V2 In principle amination of (a-al1yl)palladium complexes constitutes an allylic amination of an olefin since the a-allyl complex can be prepared directly from the olefin (eq 1). Dialkylamination of
preformed (a-ally1)palladium complexes has been dem~ n s t r a t e dand , ~ a preliminary stereochemical study indicate~ that ~ external trans attack by dialkylamine takes place. The stereochemical conclusion was based upon the fact that 3,6-bis(dimethylamino)cyclohexenewas formed by palladium-assisted diamination of l,&cyclohexadiene, a result of trans aminopalladation of one of the double bonds followed by external trans attack on the intermediate (a-ally1)palladium ~ o m p l e x .Studies ~ by Trost et al. suggest that a competing cis attack by amine also OCCLUS.~ Thus, palladium-catalyzed dialkylamination of cis- and trans-3-acetoxy-5-carbomethoxycyclohexenes in each case gave a cis-trans mixture of amine products. To account for these results, it was suggested5 that about a third of the product arises from cis migration of the coordinated amine from palladium to carbon and the rest via external trans attack. In view of extensive applications in organic synthesis of reactions involving nucleophilic attack on (a-ally1)palladium c ~ m p l e x e sfurther , ~ ~ studies on the mechanism of (1) (a) Sharpless, K. B.; Hori, T.; Truesdale, L. L.; Dietrich, C. 0. J. Am. Chem. SOC.1976, 98, 269. (b) Sharpless, K. B.; Hori, T. J. Org. Chem. 1976,41,176. (c) Schonberger, N.; Kresze, G. Justw Liebigs Ann. Chem. 1975, 1725. (2) (a) Keck, G. E.; Yates, J. B. Tetrahedron Lett. 1979, 4627. (b) Toshimitsu, A.; Owada, H.; Aoai, T.; Uemura, S.;Okano, M. J. Chem. SOC., Chem. Commun. 1981,546. (c) Toshimitau. A,; Aoai, T.; Swada, H.; Uemura, S.; Okano, M. J. Org. Chem. 1981, 46, 4727. (3) Akermark, B.; Zetterberg, K. Tetrahedron Lett. 1976, 3733. (4) Akermark, B.; Blckvall. J. E.; Lowenberg, A.; Zetterberg, K. J. Organomet. Chem. 1979, 166, C33. (5) Trost, B. M.; Keinan, E. J. Am. Chem. Soc. 1978, 100, 7779. (6) (a) Trost, B. M. Acc. Chem. Res. 1980, 13, 385. (b) Tsuji, J. 'Organic Synthesis with Palladium Compounds"; Springer-Verlag: Berlin, 1980. (c) Trost B. M. Tetrahedron 1977, 33, 2615; Pure Appl. Chem. 1979,51,187. (7) (a) Trost, B. M.; Verhoeven, T. R. J . Am. Chem. SOC.1976,98,630. (b) Trost, B. M.; Verhoeven, T. R. Ibid. 1978,100,3435. (c) Trost, B. M.; Keinan, E. J. Org. Chem. 1979,44, 3451. (d) Trost, B. M.; GenOt, J. P. J. Am. Chem. SOC. 1976,98,8516. (e) GenOt, J. P; Piau, F.J . Org. Chem. 1981,46, 2414.
these reactions seemed desirable. In this paper we have examined the stoichiometric dialkylamination of a (a-al1yl)palladium complex and found that the major pathway is external trans attack by an amine nucleophile. Under certain conditions up to 14% cis addition takes place.
Results The (a-ally1)palladium complex 1, prepared by methoxypalladation of 1,3-cyclohexadiene (see Experimental Section), was used as a substrate for the mechanistic studies made here. We have previously established'O the trans relationship between the methoxy group and the palladium atom in 1, making this complex a suitable substrate for stereochemical studies. Treatment of 1 with equimolar amounts of AgBF, and PPh3in T H F followed by addition of dimethylamine resulted in the precipitation of palladium black and formation of &-3-(dimethylamino)-6-methoxycyclohexene(2) as the main product. Hso
Ag BF4 - Wh3
QoMe MqNH
J1,3
-
2 . 0 HZ
J 2 , 3 = 2.0 HT
b*qeNt4ez Me9
J3,4a= 9.0 HZ
The cis configuration of 2 was established by 'H NMR spectroscopy. The coupling constants J3,4a = 9.0 Hz and J3,&= 5.4 Hz and J5a,6 = J5e,6= 3.5 Hz are only consistent with a cis configuration, with a preferred conformation in which the amino group is equatorial and the methoxy group is axial. The formation of the cis isomer 2 from 1 thus shows that the amine has attacked the a-allyl group from the face opposite to that of the metal (trans attack). The analogous amination of 1 in T H F using diethylamine also gave the cis-methoxy amine 3 as the major product by an external trans attack. However, careful analysis of the reaction mixture revealed the presence of two other isomeric products. Separation of these products (8)(a) Backvall, J. E.; Nordberg, R. E. J . Am. Chem. SOC.1981,103, 4959. (b) BBckvall, J. E.; Nordberg, R. E.; Nystram, J. E. Tetrahedron Lett. 1982, 23, 1617. (c) BHckvall, J. E.; Nystrom, J. E. J. Chem. SOC., Chem. Commun. 1981,59. (d) Biickvall, J. E.; Nordberg, R. E.; Nystrom, J. E.; Hogberg, T.; Ulff, B. J. Org. Chem. 1981, 46, 3479. (9) (a) Temple, J. S.; Riediker, J.; Schwarz, J. J.Am. Chem. SOC.1982, 104, 1310. (b) Hayasi, Y.; Riediker, M.; Temple, J. S.;Schwartz, J. Tetrahedron Lett. 1981, 2629. (10) Bickvall, J. E.; Nordberg, R. E.; Bjorkman, E. E.; Moberg, C. J. Chem. Soc., Chem. Commun. 1980, 943. (11) Jackman, L. M.; Sternhell, S."Applicationof Nuclear Magnetic
Resonance Spectroscopy in Organic Chemistry"; Pergamon Press: Oxford, 1969.
0276-733318312302-l625$01.50/0 0 1983 American Chemical Society
1626 Organometallics, Vol. 2, No. 11, 1983
Backuall et al.
Table I. Nucleophilic Addition of Amines t o 1
GC yield,a % entry
PPh,
1
1
amine Et,"
2
4
Et,"
3
AgBF,
4
solv
Me,"
THF THF THF
Et,"
benzene
1
Et,"
THF
4
1
Et,"
THF
7
4
1
Et,"
benzene
8
10
1
Et,"
THF
4
4
5
1
6
% cis addition product
time, h
3
4
5
0.3 96 0.3 1.5 24 0.3 2 24 48 0.3 3.5 20 216 0.3 2 4 24 0.3 1 4 24 120 0.3 3 24 4.5
25 51 82 82 85 75 72 79 76 90 87 82 83 56 76 74 87 66 67 67 62 24 65 62 58 57
