Hansley-Prelog acyloin condensation

The Hansley-Prelog-Acyloin condensation , Prelog-Stoll cyclization or Bouveault-Hansley-Prelog-Stoll acyloin synthesis is a name reaction in organic chemistry . It is used for the synthesis of cyclic acyloins ( α - hydroxyketones ) from esters of higher dicarboxylic acids . The reaction is one of the radical reactions and is the intramolecular variant of the acyloin condensation .

It was first presented in 1935 by VL Hansley and expanded around 1940–1950 by the Swiss chemist Vladimir Prelog (1906–1998).

Overview reaction

The acyloin 2 is formed from the dicarboxylic acid diester 1 with ring closure . The chain length of the dicarboxylic acid diester is variable. The reaction of unsaturated dicarboxylic acid diesters is also possible.

The radicals R are organyl radicals , e.g. B. alkyl radicals. The blue marked bond in acyloin is the newly formed carbon-carbon bond, which leads to ring closure.

Reaction mechanism

The following mechanism is described in the literature.

First, the dicarboxylic acid diester reacts with sodium to form the radical anion 3 . In the next step, the intramolecular dimerization leads to ring closure and the dianion 4 is formed. Through electron rearrangements, two alcoholate residues are split off and the diketone 5 is formed . A further radical formation and subsequent dimerization in the next two steps lead to the formation of the anion 6 . The enediol 7 is obtained by protonation . 7 is in equilibrium with acyloin 8 via the keto-enol tautomerism .

Individual evidence

^ ^A ^b ^c Zerong Wang: Comprehensive Organic Name Reactions and Reagents , Wiley, 2010, ISBN 978-0-47063885-9 , pp. 1317-1320, doi: 10.1002 / 9780470638859 .
^ VL Hansley: The Preparation of High Molecular Weight Acyloins In: Journal of the American Chemical Society 57, 1935, pp. 2303-2305, doi: 10.1021 / ja01314a076 .
^ V. Prelog, K. Schenker and HH Günthard: On the knowledge of the carbon ring. Part 60. For knowledge of the ten ring In: Helvetica Chimica Acta 35, 1952, pp. 1598–1615, doi: 10.1002 / hlca.19520350526 .

[wang-1] A ^b ^c Zerong Wang: Comprehensive Organic Name Reactions and Reagents , Wiley, 2010, ISBN 978-0-47063885-9 , pp. 1317-1320, doi: 10.1002 / 9780470638859 .

[2] VL Hansley: The Preparation of High Molecular Weight Acyloins In: Journal of the American Chemical Society 57, 1935, pp. 2303-2305, doi: 10.1021 / ja01314a076 .

[3] V. Prelog, K. Schenker and HH Günthard: On the knowledge of the carbon ring. Part 60. For knowledge of the ten ring In: Helvetica Chimica Acta 35, 1952, pp. 1598–1615, doi: 10.1002 / hlca.19520350526 .