Page 348 - Advanced Organic Chemistry Part B - Reactions & Synthesis

320 a discussion of this reaction.) In Entry 17, the primary iodo substituent was replaced by
a benzoate group. In Entry 18, the reactant was prepared with high anti selectivity by
CHAPTER 4
an auxiliary-directed aldol reaction. The acyloxazolidinone auxiliary then participated
Electrophilic Additions in the iodocyclization and was cleaved in the process.
to Carbon-Carbon
Multiple Bonds
I
H OH H OH
I
CH 3 CH 3 CH 3 CH 3
PhCH O O PhCH O O
2
2
CH 3 Oxaz CH 3 O
The reaction in Entry 19 was effected using NBS.

4.2.2. Sulfenylcyclization and Selenenylcyclization

Reactants with internal nucleophiles are also subject to cyclization by electrophilic
sulfur reagents, a reaction known as sulfenylcyclization. 92 As for iodolactonization,
unsaturated carboxylic acids give products that result from anti addition. 93

CO H O
2
O
PhSCl
N
Et 3
PhS 70%
SPh
PhSCl
N
Et 3
CO H O
2
O 95%
Similarly, alcohols undergo cyclization to ethers.
The corresponding reactions using selenium electrophiles are called selenenylcy-
clization. 94 95 Carboxylate (selenylactonization), hydroxy (selenyletherification), and
nitrogen (selenylamidation) groups can all be captured in appropriate cases.

PhSeCl
CH CO H
2
2
PhSe O O 93%
Internal nucleophilic capture of seleniranium ion is governed by general principles
96
similar to those of other electrophilic cyclizations. The stereochemistry of cyclization
can usually be predicted on the basis of a cyclic TS with favored pseudoequatorial
orientation of the substituents.
92 G. Capozzi, G. Modena, and L. Pasquato, in The Chemistry of Sulphenic Acids and Their Derivatives,
S. Patai, ed., Wiley, Chichester, 1990, pp. 446–460.
93
K. C. Nicolaou, S. P. Seitz, W. T. Sipio, and J. F. Blount, J. Am. Chem. Soc., 101, 3884 (1979).
94 K. Fujita, Rev. Heteroatom. Chem., 16, 101 (1997).
95 K. C. Nicolaou, S. P. Seitz, W. J. Sipio, and J. F. Blount, J. Am. Chem. Soc., 101, 3884 (1979);
M. Tiecco, Topics Curr. Chem., 208, 7 (2000); S. Raganathan, K. M. Muraleedharan, N. K. Vaish, and
N. Jayaraman, Tetrahedron, 60, 5273 (2004).
96
N. Petragnani, H. A. Stefani, and C. J. Valduga, Tetrahedron, 57, 1411 (2001).