Page 738 - Advanced Organic Chemistry Part B - Reactions & Synthesis

714 anion by 1-phenylprop-2-enyl acetate in the presence of iodide ion. In the absence of
iodide, using 2 mol % catalyst, the ratio of 2 to 3 is about 4:1. When 2 mol % iodide
CHAPTER 8 is added, only 2 is formed. This change is attributed to the involvement of a catalytic
−
Reactions Involving species in which I is present as a Pd ligand. The effect is diminished when a chelating
Transition Metals
−
diphosphine ligand is used, presumably because addition of I to the Pd ligand sphere
is prevented by the chelate.
PdCl CH 3
CH CH(CO CH ) + PhCHCH CH 2 2 Ph C(CO CH ) Ph
3
3 2
2
O CCH 3 Ph P 2 2 3 2 + 3 C(CO CH )
2
3
2
3 2
No I – 77 23
CH 3
LiI 100 0
Li(dppe) 89 11
Ref. 121
The allylation reaction has also been used to form rings. -Sulfonyl esters have
proven particularly useful in this application for formation of both medium and large
rings. 122 In some cases medium-sized rings are formed in preference to six- and
seven-membered rings. 123
O
O
Pd(PPh )
CHCH COCH CH CH CHCH O CCH 3 4
PhSO 2 2 2 2 2 2 3 O
NaH
CO CH 3
2
PhSO 2 CO CH 3
2
O CCH 3 54% + 5% of E-isomer
2
H O CH C H O
)
C 2 5 Pd(PPh 3 4 2 5
2
2
CH 3 O O SO Ph
O CH SO Ph CH 3 O 60%
2
2
The sulfonyl substituent can be removed by reduction after the ring closure (see
Section 5.6.2). Other appropriate reactants are -phenylthio nitriles, which can be
hydrolyzed to lactones. 124
(CH ) O CN NC
2 n
)
3% Pd(PPh 3 4 CH OH O
3
O CCH 3 SPh PhS O (CH 2 n O (CH )
)
2
2 n
n=8,9 n=8 95 % ~8 :1 E:Z
n=9 86 %
Allylation reactions can be made highly enantioselective by the use of various chiral
phosphine ligands. 125 Examples are included in Scheme 8.8.
121 M. Kawatsura, Y. Uozumi, and T. Hayashi, J. Chem. Soc., Chem. Commun., 217 (1998).
122
B. M. Trost, Angew. Chem. Int. Ed. Engl., 28, 1173 (1989).
123
B. M. Trost and T. R. Verhoeven, J. Am. Chem. Soc., 102, 4743 (1980); B. M. Trost and S. J. Brickner,
J. Am. Chem. Soc., 105, 568 (1983); B. M. Trost, B. A. Vos, C. M. Brzezowski, and D. P. Martina,
Tetrahedron Lett., 33, 717 (1992).
124 B. M. Trost and J. R. Granja, J. Am. Chem. Soc., 113, 1044 (1991).
125
S. J. Sesay and J. M. J. Williams, in Advances in Asymmetric Synthesis, Vol. 3, A. Hassner, ed., JAI
Press, Stamford, CT, 1998, pp. 235–271; G. Helmchen, J. Organomet. Chem., 576, 203 (1999).