DABCO-Catalyzed Coupling of Aldehydes with Activated Double Bonds. 4. Stereoselective Synthesis of Trisubstituted Olefins and Terpenoid Building Blocks via 2-(Hydroksyalkyl)-2-propenoic Esters.

Article abstract of DOI:10.1021/jo00220a034

A variety of 2-(hydroksyalkyl)-2-propenoic esters 16a-g has been prepared in high yield by DABCO-catalyzed coupling of aldehydes 14a-g with methyl acrylate.The product esters 16a-g are useful building blocks in syntheses which undergo regioselective and Z-selective SN2 reactions with N-bromosuccinimide/dimethyl sulfide and N-chlorosuccinimide/dimethyl sulfide to furnish (Z)-2-(bromomethyl)-2-alkenoic esters 17a-g and (Z)-2-(chloromethyl)-2-alkenoic esters 18b,c,d, respectively.Similarly, the derived allylic acetates 21g,h, and also allylic bromide 17g react with lithium triethylhydridoborate via mechanism SN2' to give (E)-2-methyl-2-alkenoic esters 22g,h and respectively, 2-methylenealkanoic esters 20g.Methyl (Z)-6,6-(ethylenedioxy)-2-methyl-2-heptenoate (22h) has been prepared as an intermediate en route to the norsesquiterpenoid ketone 23.The allylic bromides 17d,e,f also furnish (Z)-6-methyl-5-<(trimethylsilyl)methyl>-4-heptene-1,6-diol (19a), (Z)-2-methyl-3-<(trimethylsilyl)methyl>-3-octene-2,7-diol (19e), and (Z)-7-methyl-6-<(trimethylsilyl)methyl>-5-octene-1,2,7-triol (19f), which are terpenoid building blocks.