Ethers haloalkenyl

Cinnamyl—sesamol ethers, eg (35), are useful as insect chemosterilants (111). 3,4-Methylenedioxyphenyl-3-halo-2-propynyl ethers (36, X = halogen) are synergists for carbamate insecticides (112). HaloaLkyl or haloalkenyl ethers, eg (37), show acaricidal and insect juvenile hormone activity (113). The first total synthesis of gibbereUic acid was from 2-methoxy-6-aLkoxyethyl-l,4-benzoquinone, a derivative of hydroxyhydroquinone (114). 

The most general and well-developed procedures for the preparation of acetylenic ethers are based on dehydrohalogenation or dehalogenation of various haloacetals (for example, acetals of chloroacetaldehyde 52) or haloalkenyl ethers 53 (equation 34) . The first product in these eliminations usually is alkoxyacetylide 54 which can be subsequently quenched with a variety of electrophiles such as water, alkyl halides, ketones, etc to give the final product 55. 

Dehydrohalogenation or dehalogenation of haloalkenyl ethers is probably the most universal approach to alkoxyacetylenes . During the last 10 years this approach has been significantly improved and applied to the preparation of various acetylenic ethers. In contrast to older procedures, in which NaOH or NaNH2 are used as bases, these new methods usually employ alkyllithium or potassium hydride. In 1985 Smithers" " developed a procedure based on the reaction of a-chloro-jS,j5-dibromovinyl ethers 59 with butyllithium (equation 36). In contrast to previous methods, the first step of this reaction is metallation... 

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