1,2-Wittig rearrangement

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1,2 WITTIG REARRANGMENT

1,2-Wittig rearrangement is a chemical reaction that involves the rearrangement of a alkoxide adjacent to an ether into a carbonyl compound through the action of a phosphonium ylide. This reaction is named after the German chemist Georg Wittig, who is also known for the Wittig reaction, a widely used method for the synthesis of alkenes. The 1,2-Wittig rearrangement is a valuable transformation in organic chemistry for the synthesis of complex molecules from simpler precursors.

Mechanism

The mechanism of the 1,2-Wittig rearrangement involves several key steps. Initially, a phosphonium ylide is formed by the reaction of a phosphonium salt with a strong base. This ylide then reacts with an alkoxide adjacent to an ether, leading to the formation of a betaine intermediate. The betaine undergoes rearrangement to form an oxaphosphetane, which subsequently collapses to yield the carbonyl compound and a phosphine oxide.

Applications

The 1,2-Wittig rearrangement has been applied in the synthesis of various carbonyl compounds, including ketones, aldehydes, and esters. It is particularly useful in the synthesis of complex natural products and in the modification of steroids and terpenes. The ability to form carbonyl compounds from alkoxides adjacent to ethers provides a versatile tool for the construction of complex molecular architectures.

Variants

Several variants of the 1,2-Wittig rearrangement exist, including the Ireland-Claisen rearrangement, which involves the use of silyl ethers as substrates, and the Johnson-Claisen rearrangement, which uses acetates as leaving groups. These variants expand the scope of the reaction to include a wider range of substrates and functional group transformations.

See also

• Wittig reaction
• Claisen rearrangement
• Organic synthesis
• Chemical synthesis