Phosphines spirocyclic

Spirooxyphosphoranes 166 were obtained by the cyclodehydration of ortho-carboxyarylmethyl phosphine oxides under acidic conditions (Equation 15) to give 166 (X = Y = 0) in which the oxygens occupy the axial positions. Related spirocyclic azoxyphosphoranes 166 (X = NH, NMe) were synthesized from amidoarylmethyl phosphine oxides and trifluoracetic acid <1996PS241>. 

The reactions of phosphine with a-branched aldehydes follow a different pathway. They lead to the formation of stable, heterocyclic, secondary phosphines of the following type, J With suitable dialdehydes, spirocyclic phosphonium salts are obtained these are very difficult to prepare by... 

Cyciopentanones. I hc cyclization of 4-pentenals to cyclopentanones catalyzed by Wilkinson s catalyst (4, 560) has been improved considerably by modification of the phosphine ligands.1 Catalysts containing tri-p-tolylphosphine. tri-p-anisylphos-phine, and lris(p-dimethylaminopheny )phosphine are particularly useful. Simple cyclopentanones can he prepared in high yields. The reaction also provides a route to spirocyclic and bicyclic ketones (equations I and II). Unfortunately this method is not applicable to synthesis of larger rings. 

A lower range of ee-values was obtained using chiral carbene ligand 17 [15], iPr-DuPHOS (18) [16] and diethyleneamine-bridged phosphoramidite 19 [17]. To date, the best enantioselectivities using this protocol were achieved with Kondo s hemilabile TADDOL-based phosphine-phosphine oxide 20 [18] and Zhou s spirocyclic phosphite 21 (Figure 8.3) [19]. 

With tris(dimethylamino)phosphine and ethanolamine or carboxylic add hydrides, spirocyclic phosphoranes are obtained. 

Several other mechanistically distinct metal-catalyzed dearomatization procedures have been reported, and almost all involve phenol or naphthol derivatives undergoing dearomatization via intramolecular transformations. Intramolecular Pd- and Rh-catalyzed C4-arylation and alkylation of /)ara-substituted phenols has been used to construct compounds of general structure 82 (Fig. 15.1) [86]. These reactions rely on generation of electrophilic aryl or alkyl o-metal complex intermediates that participate in tandem C4 metalation-reductive elimination with an attached phenol. Ruthenium- and Pt-catalyzed reactions of naphthalenes and alkynes deliver spirocyclic products such as 83 [87, 88]. An asymmetric intramolecular naphthalene dearomatization catalyzed by Pd(0)-phosphine complexes has been used to prepare carbazole derivatives 84 in good enantiomeric excess from l-(AI-2-bromophenyl)aminonaphthalene precursors [89]. 

Also, spirocycles are obtained in the phosphine-catalyzed [3-1-2] cycloaddition of cyclo-hexenone derivatives with allenoates. This reaction is utilized in the total synthesis of (—) hinesol . ... 

The triphenylphosphine-catalyzed [3+2] cycloaddition reaction of allenyl ketones to cyclic enones affords spirocyclic adducts. For example, from 336 and the allenyl methyl ketone 337 the cycloadducts 338 and 339 (ratio 55 45) are obtained in 84 % yields. Using chiral phosphines, ees of 53-71 % are observed. 

Another [3-1-2] cycloaddition was reported by Marinetti in 2009 [17], 3-Benzylideneindolin-2-ones 17a reacted with allenes 35, in the presence of a catalytic amount of chiral phosphine V (Scheme 10.9). The reaction afforded the desired spirocyclic indanones 36 in good yields and excellent enantiomeric excesses with aromatic or heteroaromatic moieties on the exocyclic double bond through the catalytic pathway, as shown in Scheme 10.10. Remarkably, allenylphosphonates acted as suitable allene counterparts to afford the corresponding phosphonate... 

A related approach for the synthesis of spirocyclopenteneoxindoles was developed by Barbas and coworkers. Chiral diphosphines catalyzed the [3+2] cycloaddition between the A-protected methyleneindolin-2-ones 17b and the Morita-Baylis-Hillman (MBH) carbonates 37 [18]. This reaction was initiated by the displacement of the carbonate moiety by the phosphine VI, an addition-elimination mechanism, which was followed by the deprotonation to afford ylide 39. A regioselective nucleophilic addition on 17 by 39, followed by an intramolecular conjugate addition, afforded intermediate 40 that, after elimination of PR3, delivered the corresponding spirocycle 41 (Scheme 10.11). 

This strategy was used to synthesize spirocyclopenteneoxindoles, as well as stereodefined cyclopentenes. Likewise, Hu reported a [3 -f 2] annulation reaction of 2-atylideneindane-l,3-diones with MBH carbonates that proceeded smoothly in the presence of a multifunctional thiourea-phosphine catalysts to produce the corresponding quaternary carbon centered spirocyclic cyclopentenes. A phosphine-triggered tandem [3 + 4] annulation reaction between MBH carbonates and 1,4-diheteroatom dinucleophiles was described, which provided access to saturated seven-membered 1,4-heterocycles. Analogously, MBH carbonates were used as C3 synthons in asymmetric [3 + 2] annulation reactions for the asymmetric synthesis of 3-spirocyclopentene-2-oxindoles. Another kind of annulation reaction for the construction of highly functionalized stereodefined cyclopentene skeletons involved a Rauhut-Currier Domino Reaction. Finally, an efficient asymmetric [3 + 2] cycloaddition reaction between MBH carbonates of isatins and... 

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