Equilibrium between a vinylogous ylide and a phosphonium dienolate zwitterion: vinylogous Wittig olefination versus vinylogous aldol-type reaction

Abstract

This paper describes the equilibrium established between a phosphonium dienolate zwitterion and a vinylogous phosphorus ylide, and their reactions with aldehydes. The reactions between ethyl 2-methyl-2,3-butadienoate and various aldehydes occur through either a phosphonium dienolate or a vinylogous ylide intermediate, depending on the presence/absence of a Lewis acid and the nature of the phosphine. We observed a rare vinylogous Wittig olefination from the reaction between ethyl 2-methyl-2,3-butadienoate and an electron-deficient aromatic aldehyde in the presence of a stoichiometric amount of an electron-deficient triarylphosphine and a catalytic amount of a Lewis acid (e.g., BF 3 ·Et 2 O). On the other hand, the use of triphenylphosphine, in the absence of a Lewis acid, facilitated vinylogous aldol addition, accompanied by a rare 1,2-aryl phosphorus-to-carbon migration.

Phosphine-Catalyzed β′-Umpolung Addition of Nucleophiles to Activated α-Alkyl Allenes

“…The observed activation of the β′-carbon atom of α-alkyl allenoates stems from the equilibrium between the β-phosphonium dienolate and the vinylogous ylide (see the mechanistic discussion below). 4d,f,g …”

“…A well-established equilibrium between the phosphonium enolate 9 and the vinylogous phosphorous ylide 10 is facilitated through proton transfer steps. 4d,f,g Deprotonation of the pronucleophile by the ylide 11 forms the phosphonium enoate electrophile 12 . Conjugate addition of the anionic nucleophile to the enoate and subsequent β-elimination of the phosphine yields the observed β′-umpolung addition product.…”

Enantioselective N‐Heterocyclic Carbene Catalyzed Cyclopentene Synthesis via the β‐Azolium Ylide

“…More than 45 years ago,w ork from Morita [1a] and Baylis/ Hillman [1b,c] led to the discovery that simple conjugate acceptors could be coupled with aldehydes by using catalytic phosphine or amine Lewis bases (Scheme 1a). Key mechanistic features of these,a nd the related Rauhut-Currier reaction, [1o,p] involve 1,4-addition of the Lewis base to give enolate 1,which is alkylated, and following elimination of the catalyst, provides a-substituted products (2). Finer mechanistic detail, enantioselective variants,and more sophisticated reaction designs have since allowed these reactions to enter the lexicon of synthesis.…”

“…[2a] It was proposed that following 1,4addition of the Ph 3 P, alcohol-mediated tautomerization gives the novel b-phosphonium ylide (4!5), which goes on to provide 3. [2] More recently,F ua nd co-workers reported the N-heterocyclic carbene (NHC)-catalyzed formation of cyclopentane 6 via the related b-azolium ylide 7 (Scheme 1c). [3] This species,atype of deoxy-Breslow intermediate, [4] is analogous to adducts discovered by Enders et al in stoichiometric reactions of the triphenyltriazolium carbene with conjugate acceptors.…”

Progress on Vinylogous Organic Reactions of Allylic Phosphorus Ylides with Carbonyl Compounds

“…通过叔膦与亲电性底物原位形成的烯丙基磷叶立 德具有丰富的反应性, 相关研究在近年来引起了化学家 浓厚的研究兴趣 [14] . 贺峥杰小组 [15] 和 Kwon 小组 [16] 值得一提的是, 与 γ-甲基联烯酸酯不同, γ-苄基或 γ-甲氧羰甲基联烯酸酯与醛或水杨醛反应时, 未能发生叔 膦催化的环化反应, 而是经原位形成的烯丙基磷叶立德 17 与醛的 Wittig 反应, 生成多取代共轭二烯烃(Scheme 10) [19,23] . 这种反应性的差异可能源于苯基或酯基的共 轭及立体位阻效应, 促使烯丙基磷叶立德 17 主要通过 α 位碳对醛进行亲核进攻, 从而发生经典的 Wittig 反应.…”