ADDITION OF A FUNCTIONALIZED ISOPRENE UNIT TO AN ALLYL ALCOHOL .I. SYNTHESIS OF BETA-SINENSAL AND RELATED TOPICS

Full details of the synthesis of β-sinensal (16) in one step from 2-methyl-6-methyleneocta-2,7-dienol (12) and 1-ethoxy-2-methylbuta-1,3-diene (10) are given. The reaction is a general one for allyl alcohols, and its stereochemistry has been examined using 2-methylbut-2-enol (19), nerol (26), and geraniol (27). The cis alcohol (nerol) leads to a trans-double bond in the product to the extent of about 70%, the trans alcohol leading mainly to a cis product. The double “Claisen-Cope” type rearrangement involved occurs to only a minor extent when 1-ethoxy-buta-1,3-diene (9) is used, the intermediate formed after the first rearrangement of the enol ether being stabilized by hydrogen rearrangement to give an α.β-unsaturated aldehyde which cannot react further. © 1969, American Chemical Society. All rights reserved.