The Dienolate [2,3]-Wittig Rearrangement – Diastereoselective Synthesis of Highly Functionalized Tertiary Alcohols

The Ester Dienolate [2,3]‐Wittig Rearrangement — Development, Opportunities, and Limitations.

“…Since we failed to mesylate the tertiary hydroxy group, thionyl chloride in pyridine was used for the elimination leading to a mixture of the a,b-and b,g-unsaturated esters 10 and 11. 15,17,18 The non-conjugated, b,gunsaturated ester 10 was preferentially formed under the reaction conditions depicted in Scheme 7. The regioisomers 10 and 11 may be separated by careful flash chromatography.…”

“…The related substrate 10,11e containing an E-configured allylic ether double gave access to the syn-configured rearrangement product 9e (Scheme 11). 18 1,5-Hexadienes 9f,g were also made accessible by this procedure. 18 The rearrangement proceeded at low temperature in the absence of donor solvents or metal salts.…”

“…18 1,5-Hexadienes 9f,g were also made accessible by this procedure. 18 The rearrangement proceeded at low temperature in the absence of donor solvents or metal salts. As mentioned above, the (-)-menthyl-induced diastereoselectivity was disappointingly low.…”

ChemInform Abstract: The Sequential Ester Dienolate [2,3]‐Wittig/3‐oxy‐Cope Rearrangement. New Access to Substituted α‐Keto Esters.

“…The 2-alkoxycarbonyl-substituted allyl vinyl ethers 1a-i were prepared following our established aldol condensation strategy. 1,7 Treating the a,b-unsaturated esters 1a-f with LDA at -78°C in THF followed by warming the reaction mixture to room temperature afforded the hexadienes 4a-f (Scheme 2, Table 1).…”

“…The stereochemical result of the rearrangement can be explained by our previously suggested transition state model for the dienolate [2,3]-Wittig rearrangement. 7 We propose a bicyclo[3.3.0]octane-type transition state 6 based on a Zconfigurated chelated dienolate 3 with the central atom of the allylic ether moiety directed toward the lithium cation (Scheme 1). This model offers an explanation for the relationship between the allylic ether double bond configuration in substrate 1 and the relative configuration of the major diastereomer 4 from the [2,3] rearrangement (E to syn and Z to anti).…”