Westphalen rearrangement

The Westphalen rearrangement or Westphalen-Lettré rearrangement is a name reaction in organic chemistry . This name reaction involves a rearrangement of a methyl group and the associated formation of a double bond. It was discovered in 1914 by the German chemist Theodor Westphalen († 1915) and examined in more detail by Hans Lettré in 1937 .

Overview reaction

During this rearrangement reaction, a methyl group migrates , splitting off water , and a double bond is also formed.

Here, R ¹ and R ² can be any organic radicals. An example of a molecule would be cholestanetriol diacetate.

Reaction mechanism

This reaction mechanism is a suggestion from the book "Comprehensive Organic Name Reactions and Reagents":

By adding an acid , the hydroxyl group of the alcohol ( 1 ) can now be protonated , which then splits off the good leaving group water . The tertiary carbenium ion ( 2 ) is stabilized by the three adjacent alkyl groups due to the + I effect . The methyl group can now make the electrons available by migrating over to the carbenium ion ( 3 ). The now also tertiary carbenium ion can form a double bond by splitting off a proton on an adjacent carbon atom, it is formed ( 4 ).

Individual evidence

↑ Z. Wang (Ed.): Comprehensive Organic Name Reactions and Reagents, 3 Volume Set . John Wiley & Sons, Hoboken, New Jersey 2009, ISBN 978-0-471-70450-8 , p. 2988.
↑ ^a ^b Theodor Westphalen: On the effect of benzoperic acid on cholesterol . In: Reports of the German Chemical Society . tape 48 , no. 1 , January 1915, p. 1064-1069 , doi : 10.1002 / cber.191504801149 ( PDF ).
^ H. Lettré, M. Müller: Some conversions on the cholestantriol . In: Reports of the German Chemical Society . tape 70 , no. September 9 , 1937, p. 1947–1952 , doi : 10.1002 / cber.19370700918 ( PDF ).

↑ M. Windholz (Ed.): The Merck Index . Ninth Edition. Merck & Co., 1976, ISBN 978-0-911910-26-1 , p. ON-93.

↑ Z. Wang (Ed.): Comprehensive Organic Name Reactions and Reagents, 3 Volume Set . John Wiley & Sons, Hoboken, New Jersey 2009, ISBN 978-0-471-70450-8 , p. 2990.

[1] Z. Wang (Ed.): Comprehensive Organic Name Reactions and Reagents, 3 Volume Set . John Wiley & Sons, Hoboken, New Jersey 2009, ISBN 978-0-471-70450-8 , p. 2988.

[Westphalen-2] Theodor Westphalen: On the effect of benzoperic acid on cholesterol . In: Reports of the German Chemical Society . tape 48 , no. 1 , January 1915, p. 1064-1069 , doi : 10.1002 / cber.191504801149 ( PDF ).

[3] H. Lettré, M. Müller: Some conversions on the cholestantriol . In: Reports of the German Chemical Society . tape 70 , no. September 9 , 1937, p. 1947–1952 , doi : 10.1002 / cber.19370700918 ( PDF ).

[Windholz_1477-4] M. Windholz (Ed.): The Merck Index . Ninth Edition. Merck & Co., 1976, ISBN 978-0-911910-26-1 , p. ON-93.

[Wang_1477-5] Z. Wang (Ed.): Comprehensive Organic Name Reactions and Reagents, 3 Volume Set . John Wiley & Sons, Hoboken, New Jersey 2009, ISBN 978-0-471-70450-8 , p. 2990.