Page 602 - Advanced Organic Chemistry Part B - Reactions & Synthesis

576 step. Entry 8 involves another fluorinated reactant. The reaction is an adaptation of
the rearrangement of -amido ester enolates, as discussed on p. 572, and involves a
CHAPTER 6
chelated enolate. Entry 9 is another example of this type of reaction. Use of quinine
Concerted or quinidine with the chelating metal leads to enantioselectivity.
Cycloadditions,
Unimolecular Entries 10 to 15 involve use of the Ireland-Claisen rearrangement in multistep
Rearrangements, and syntheses. An interesting feature of Entry 11 is the presence of an unprotected ketone.
Thermal Eliminations
The reaction was done by adding LDA to the ester, which was premixed with TMS-Cl
and Et N. The reaction generates the E-silyl ketene acetal, which rearranges through
3
a chair TS.
CH CH CH 3CH CH CH
3 3 2 3 3
CH CH CH CH
3 CH 3 3 3
3
R
CH R
CH 2 O O OTBDMS O TSMO C
3 2 O
TSMO O
OTMS
96:4 dr
Entries 12 to 15 are examples of -alkoxy (protected glycolate) esters. These reactions
proceed through chelated TSs. (See the discussion on p. 571.) The TS for Entries 13
and 14 are shown below.

H O Li PhCH O H Li H
2
O
O O TBDPSO
C H O O CH 3 MeO O O
2 5
C H PhCH 2
2 5
Entry 15 also demonstrates the suprafacial specificity with a cyclic allylic alcohol.

6.4.2.4. Claisen Rerrangements of Ketene Aminals and Imidates. A reaction that
is related to the orthoester Claisen rearrangement utilizes an amide acetal, such as
dimethylacetamide dimethyl acetal, in the exchange reaction with allylic alcohols. 257
The products are
-unsaturated amides. The stereochemistry of the reaction is
analogous to the other variants of the Claisen rearrangement. 258

OCH OCH
3 3
RCH CHCH OH + (CH ) NCOCH 3 (CH ) NCOCH CH CHR (CH ) NCOCH CH CHR
2
3 2
2
3 2
3 2
2
CH 3 CH 3 CH 2
O
(CH ) NCCH CHCH CH
3 2 2 2
R
257 A. E. Wick, D. Felix, K. Steen, and A. Eschenmoser, Helv. Chim. Acta, 47, 2425 (1964); D. Felix,
K. Gschwend-Steen, A. E. Wick, and A. Eschenmoser, Helv. Chim. Acta, 52, 1030 (1969).
258
W. Sucrow, M. Slopianka, and P. P. Calderia, Chem. Ber., 108, 1101 (1975).