Bridging the Final Gap in Stereocontrolled Wittig Reactions: Methoxymethoxy-Armed Allylic Phosphorus Ylides Affording Conjugated Dienes with Highcis Selectivity

Abstract

After treatment with an appropriate base (butyllithium or sodium amide), 2-alkenyltris(2-methoxymethoxyphenyl)phosphonium salts carrying an allyl, crotyl, or prenyl (3-methyl-2-butenyl) side chain condense with saturated or unsaturated aldehydes to give conjugated dienes with Z/E ratios ranging from 90:10 to > 99:1 and averaging 96:4. Owing to steric congestion, yields are only moderate (on average 41%; extremes 10-79%). The nonvolatile tris(2-methoxymethoxyphenyl)phosphine oxide by-product can be readily isolated and reduced to recover the phosphane starting material, or it may be hydrolyzed to the water-soluble tris(2-hydroxyphenyl)phosphine oxide.

Gold(I)‐Catalyzed Intermolecular Hydroarylation of Alkenes with Indoles under Thermal and Microwave‐Assisted Conditions

“…As depicted in Scheme , this gold‐catalyzed isomerization reaction works well for dienes bearing electron‐donating and electron‐withdrawing substituents. According to the literature,21 Z aryl dienes can be synthesized by Wittig reactions with bulky phosphonium salts. Exclusive Z products could be prepared in low yields at low temperature (−100 °C) by using a strong base such as butyllithium.…”

A Wittig Reaction with 2-Furyl Substituents at the Phosphorus Atom: Improved (Z) Selectivity and Isolation of a Stable Oxaphosphetane Intermediate

“…The Wittig reaction is one of the most powerful methods for the preparation of carbon−carbon double bonds and is used as a key step in many natural product syntheses1 as well as in industrial processes 2. The main advantages of this reaction are the regioselective formation of the double bond at the position of the former carbonyl group and the potential to control the stereoselectivity by application of particular reaction conditions 3. Because of its synthetic importance, the mechanism of the Wittig reaction was long hotly contested.…”

Highly Stereoselective and General Synthesis of (E)‐Stilbenes and Alkenes by Means of an Aqueous Wittig Reaction

“…Chemoselective deprotonation at the benzylic15a position (b) over the alkyl positions (a) in a trialkyl(benzyl)phosphonium salt was reported in organic media. Similar chemoselectivity was also demonstrated with trialkyl(allyl)phosphonium salts 15b–15d. The use of trialkylphosphane‐derived ylides in Wittig olefination is of limited applicability but typically provides a higher ratio of ( E )‐olefins 4.…”