Rearrangement

1. BY
Dr. Gurumeet.C.Wadhawa
DEPARTMENT OF CHEMISTRY
K. B. P. College,Vashi,Navimumbai
Lossen Rearrangement

2. PUMMERER REARRANGEMENT
In 1909, R. Pummerer observed that by heating phenylsulfinylacetic acid
with mineral acids (e.g., HCl, H2SO4), thiophenol and glyoxylic acid
were formed.1 Later this transformation was shown to be general, and
today the formation of α-substituted sulfides from the corresponding
sulfoxides is referred to as the Pummerer rearrangement.

4. The general features of the reaction are:
1) the sulfoxide substrates must have at least one hydrogen atom at their α
position;
2) 2) acetic anhydride (Ac2O) is the most widely used activating reagent for the
rearrangement, and it is often applied as the solvent in combination with othe
solvents such as benzene or ethyl acetate;
3) the use of acid co-catalysts (e.g., TsOH, AcOH, TFAA) is common to minimiz
side reactions and increase the product yields;
4) Ac2O can be replaced with TFAA, which is a stronger reagent and allows fo
milder
reaction conditions;
5) the most common product of the reaction is an α-acetoxy sulfide;
6) upon acidic hydrolysis, the α-acetoxy sulfide affords a thiol and a carbony
compound that can be easily separated;
7) upon treatment with base, vinyl sulfides are formed via a β-elimination;
8) the rearrangement is regioselective when the sulfoxide has hydrogens at bot
the α- and α'-positions and the more acidic position will get preferentiall
substituted;
9) The regioselectivity can be altered by steric factors especially in cyclic systems
isomeric sulfoxides often give rise to different products; and
10) the rearrangement can take place both inter- and intramolecularly.

10. Drawbacks of the
reaction are: 1) substrates with unprotected hydroxyl or amino groups
result in side rections with the activating reagent;
2) unreactive substrates may undergo undesired sulfenic acid
elimination if harsh conditions are necessary;
3) fragmentation products are observed when stable carbocations
(e.g., allylic, benzylic) can be formed by the heterolytic cleavage of
the C-S bond; 4) when the nucleophile is a primary or secondary
alcohol, reduction of the
sulfoxide to the sulfide may occur along with the oxidation of the
alcohol (see Swern oxidation).

11. There are several
variants of the rearrangement: 1) when selenoxides are the substrates,
the seleno-Pummerer rearrangement takes place;
2) sila-Pummerer rearrangement occurs with sulfoxides bearing a TMS
group on the α-carbon, which spontaneously rearrange to α-silyloxy
sulfides, and no activating reagents are needed;
3) vinyl sulfoxide substrates may undergo the additive- and vinylogous
Pummerer rearrangement;
4) chirality transfer from enantiopure sulfoxides to the α-carbon is
possible, and it constitutes the asymmetric Pummerer rearrangement,
but this process is limited in
scope

16. References
1. Pummerer, R. Ber. 1910, 43, 140-1412. Rudolf Pummerer, born in Austria in
1882,
studied under von Baeyer, Willstätter, and Wieland. He worked for BASF for a few
years and in 1921 he was appointed head of the organic division of the Munich
Laboratory,
fulfilling his long-desired ambition.
2. Katsuki, T.; Lee, A. W. M.; Ma, P.; Martin, V. S.; Masamune, S.; Sharpless, K. B.;
Tuddenham, D.; Walker, F. J. J. Org. Chem. 1982, 47, 1373-1378.
3. De Lucchi, O.; Miotti, U.; Modena, G. Org. React. 1991, 40, 15-406. (Review).
4. Padwa, A.; Gunn, D. E., Jr.; Osterhout, M. H. Synthesis 1997, 135-1378.
(Review).
5. Padwa, A.; Waterson, A. G. Curr. Org. Chem. 2000, 4, 17-203. (Review).
6. Padwa, A.; Bur, S. K.; Danca, D. M.; Ginn, J. D.; Lynch, S. M. Synlett 2002, 851-
862.
(Review).
7. Gámez Montaño, R.; Zhu, J. Chem. Commun. 2002, 2448-2449.
8. Padwa, A.; Danca, M. D.; Hardcastle, K.; McClure, M. J. Org. Chem. 2003, 68,
929-941.
9. Suzuki, T.; Honda, Y.; Izawa, K.; Williams, R. M. J. Org. Chem. 2005, 70,
7317-7323.
10. Nagao, Y.; Miyamoto, S.; Miyamoto, M.; Takeshige, H.; Hayashi, K.; Sano, S.;
Shiro,
M.; Yamaguchi, K.; Sei, Y. J. Am. Chem. Soc. 2006, 128, 9722-9729.
11. Ahmad, N. M. Pummerer Rearrangement. In Name Reactions for