Boord Olefin Synthesis

The Boord olefin synthesis or Boord elimination is a name reaction in organic chemistry . The first report on them comes from Cecil E. Boord in 1930 . This reaction has many uses in the production of alkenes . A mixture of cis and trans alkenes is formed (R = alkyl group):

mechanism

The figure shows a postulated mechanism (R = alkyl group). The reaction is characterized by a wide range of possible applications and high yields.

An aldehyde 1 is protonated with hydrogen chloride to form 2 . A protonated hemiacetal 3 or 4 is formed with ethanol . The nucleophilic attack of a chloride ion and the elimination of water give rise to unstable chlorinated ethers 5 , from which hydrogen chloride is split off to form 6 . The halogenation of 6 (shown here with bromine as an example) provides the doubly brominated ether 8 via a bromonium ion 7 . The latter reacts with a Grignard compound to form the simply α-brominated ether 9 . By adding zinc, 9 is formed via intermediate 10 , and alkene 11 as an ( E, Z ) mixture by elimination. Zinc can also be replaced by magnesium or sodium . When using zinc, an E1cb mechanism is usually postulated.

The reaction rate of the reaction can be controlled via the length of the alkyl radical of the added alcohol . The larger this group, the slower the reaction.

Individual evidence

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. 463.
2. ↑ Jerry March (Ed.): Advanced Organic chemistry. Reactions, mechanisms, and structure. 4th Ed. John Wiley, Chichester 1992, ISBN 0-471-58148-8 .
3. ↑ ^{a b} 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. 464.
4. ↑ Jerry March (Ed.): Advanced Organic Chemistry . 3rd edition, John Wiley & Sons, New York, 1985, ISBN 0-471-88841-9 , p. 925.