The Ester Dienolate [2,3]-WittigRearrangement - Development, Opportunities, andLimitations

Abstract

T h e E s t e r D i e n o l a t e [ 2 , 3 ] -W i t t i g R e a r r a n g e m e n t Abstract: The account summarizes the development of the ester dienolate [2,3]-Wittig rearrangement as a versatile synthetic tool for the construction of highly substituted 3-alkoxycarbonyl-3-hydroxysubstituted 1,5-hexadienes. Furthermore, the account provides an insight into a novel sequential pericyclic reaction employing the 1,5-hexadienes accessible through the ester dienolate [2,3]-Wittig rearrangement.

Palladium(II)-Catalyzed Cycloisomerization of Functionalized 1,5-Hexadienes

“…Notably, the known Pd(II)-based procedures trigger double bond isomerization and, thereby, convert the initially formed methylene cyclopentanes into methyl cyclopentenes. Nonetheless, and in light of potential chemoselectivity issues with highly functionalized substrates, we elected to pursue the Pd(II)-catalyzed cycloisomerization, and for that purpose, the known 1,5-hexadiene 2a was used for the initial search of catalysts and conditions which would support methylene cyclopentane formation (Table ).…”

Palladium(II)-Catalyzed Cycloisomerization of Substituted 1,5-Hexadienes: A Combined Experimental and Computational Study on an Open and an Interrupted Hydropalladation/Carbopalladation/β-Hydride Elimination (HCHe) Catalytic Cycle

“…1,5-Hexadiene (±)- 1g . According to the general procedure for the [2,3]-Wittig rearrangement, the reaction of allyl vinyl ether 12 (1.13 g, 5.7 mmol) with ( i -Pr) 2 NH (0.96 mL, 6.8 mmol, 1.2 equiv) and n -BuLi (2.73 mL, 6.3 mmol, 1.1 equiv, 2.3 M in hexanes) in THF (11 mL + 17 mL) at −85 → −70 °C (30 min) and 0 °C (1 h) provided 1,5-hexadiene (±)- 1g (0.77 g, 3.9 mmol, 69%) after flash chromatography ( n -pentane/diethyl ether 100/1): R f 0.57 (cyclohexane/ethyl acetate 5/1); 1 H NMR (CDCl 3 , 400 MHz, δ) 1.26 (d, J = 6.3 Hz, 3H), 1.29 (d, J = 6.3 Hz, 3H), 1.77 (s, 3H), 2.38 (d, J = 13.9 Hz, 1H), 2.61 (d, J = 13.9 Hz, 1H), 3.35 (s, 1H), 4.71–4.91 (m, 2H), 5.06 (spt, J = 6.3 Hz, 1H), 5.17 (dd, J = 10.5, 1.2 Hz, 1H), 5.50 (dd, J = 17.0, 1.2 Hz, 1H), 5.99 (dd, J = 17.0, 10.5 Hz, 1H); 13 C NMR (CDCl 3 , 101 MHz, δ) 21.8 (CH 3 ), 21.9 (CH 3 ), 24.2 (CH 3 ), 46.6 (CH 2 ), 70.3 (CH), 77.5 (C), 114.8 (CH 2 ), 115.1 (CH 2 ), 139.2 (CH), 141.2 (C), 174.4 (C); 3515­(br m) (ν OH), 2980­(m), 2935­(m), 1725(s) (ν CO), 1645­(w) (ν CC), 1470­(w), 1455­(m), 1375­(m), 1275­(m) (ν C–O–C ester), 1210(s), 1145 (s), 1105(s), 1060­(m). Anal.…”

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

“…As depicted in Scheme 9, the relative configuration may be controlled through the appropriate choice of the allylic ether double bond configuration. 16 Another important observation was, that the simple diastereoselectivity of the ester dienolate [2,3]-Wittig rearrangement is influenced by steric factors. For instance, the introduction of a methyl group on the b-carbon atom of the dienolate increased the simple diastereoselectivity from anti/syn = 86:14 to >95:5 (Scheme 9).…”