Page 226 - Advanced Organic Chemistry Part B - Reactions & Synthesis

198 Lithiated N-allylcarbamates add to nitroalkenes. In the presence of (–)-sparteine,
this reaction is both diastereoselective (anti) and enantioselective. 331
CHAPTER 2
Reactions of Carbon Ar′ O 2 N R Ar′
Nucleophiles with nBuLi R
Carbonyl Compounds Ar N O 2 N N
CO C(CH ) (–)-sparteine Ar CO C(CH )
3 3
2
3 3
2
Ar′ = 4-methoxyphenyl for R = Ar = Ph, 94:6 dr; 90% e.e.
The enantioselectivity is due to the retention of the chiral sparteine in the lithiated
reagent. The adducts have been used to synthesize a number of pyrrolidine and
piperidine derivatives.
Several mixed organozinc reagents having a trimethylsilylmethyl group as the
nonreacting substituent add to enones under the influence of TMS-Br. 332 The types
of groups that can be added include alkyl, aryl, heteroaryl, and certain functionalized
alkyl groups, including 5-pivaloyloxypentyl and 3-ethoxycarbonylpropyl.
R′ TMS-Br
RZnCH 2 Si(CH ) + R R′
3 3
O THF-NMP
O
-Unsaturated aldehydes and esters, as well as nitroalkenes, can also function as
acceptors under these conditions. Dialkylzinc reagents add to -nitrostyrene in the
presence of TADDOL-TiCl . 333
2
C H
8 17
TADDOL-TiCl
(C H ) Zn + PhCH CHNO 2 2 NO 2
8 17 2
Ph
87%, 76% ee
2.6.6. Conjugate Addition of Cyanide Ion

Cyanide ion acts as a carbon nucleophile in the conjugate addition reaction. The
pK of HCN is 9.3, so addition in hydroxylic solvents is feasible. An alcoholic solution
of potassium or sodium cyanide is suitable for simple compounds.

CH
CH 3 3 CH 3
KCN, NH Cl
4
+
O EtOH H 2 O O CN O
H C CN
CH 3 3 H C
3
12% 42%
Ref. 334
Cyanide addition has also been done under Lewis acid catalysis. Triethylaluminum-
hydrogen cyanide and diethylaluminum cyanide are useful reagents for conjugate

331 T. A. Johnson, D. O. Jang, B. W. Slafer, M. D. Curtis, and P. Beak, J. Am. Chem. Soc., 124, 11689
(2002).
332
P. Jones, C. K. Reddy, and P. Knochel, Tetrahedron, 54, 1471 (1998).
333 H. Schaefer and D. Seebach, Tetrahedron, 51, 2305 (1995).
334
O. R. Rodig and N. J. Johnston, J. Org. Chem., 34, 1942 (1969).