Spiro-phosphines

Zhou et al. [99] developed a Ni-catalyzed reductive coupling of alkynes and imines with Et Zn as a reductant by using electron-rich spiro phosphine ligands, which afforded various allylic amines with high yields and excellent chemoselec-tivities. The asymmetric version of this reaction was also accomplished by using... 

Hu et al. [104] disclosed that the spiro phosphine oxide ligand (/ )-30a is highly efficient for the Pd-catalyzed Heck reaction of cyclic and heterocyclic olefins with aryl triflates. An asymmetric domino Heck cyclization was established using catalyst Pd/(/ )-30a to form fused carbo- and heterocycles with excellent stereoselectivity (Scheme 42) [105]. This method was used in a short synthesis of (-)-martinellic acid, a primary ingredient in traditional eye medicine in South America. 

Meanwhile, Fu shed light on the effectiveness of chiral spiro phosphine 15a [46] as an efficient nucleophihc catalyst for achieving the asymmetric intramolecular cyclization of hydroxyl-2-alkynoates into saturated oxygen-containing heterocycles such as tetrahydrofurans, tetrahydropyrans, and dihydrobenzopyrans (Scheme 7.27) [47]. In addition, Kwon employed this class of phosphine (15b) to gauge the... 

Scheme 20.27 Spiro-phosphine-catalyzed asymmetric annulation reactions.

Anthryl, 1-naphthyl, mesityl, and 4-quinolyl groups in 37h-k promote C/C aryl shift (see Table 2) their proclivity to migrate is far greater than expected from the electronic influence of the x-systems. This is presumably due to the intermediacy of spiro-linked benzenium betaines 30 31 , occurring in place of the carbenes otherwise encountered. The formation of phosphinic esters 42h-k is partly or completely suppressed 30). 

Hydroamination of olefins has received considerable attention this year as a route to functionalized piperidines and spiropiperidines, particularly in regard to the investigation of new catalysts. In the synthesis of spiro-piperidines, two new mild and more general intramolecular hydroamination protocols were developed this year. One protocol uses a cationic gold-phosphine complex (Au[P(fBu)2(o-biphenyl)]Cl) as the catalyst... 

Spiro-1,2-oxaphosphetes 50 can be obtained in good yield by the [2+2] cycloaddition of the cyclic phosphine oxide 49 with dimethyl acetylenedicarboxylate <00T4823>. 

Intramolecular Heck reactions.6 Heck intramolecular coupling of alkenyl or aryl iodides substituted by 3-cycloalkenyl group is an attractive route to fused, spiro, and bridged polycyclic products. Coupling is achieved with a Pd-phosphine catalyst such as Pd[P(QH5),]4 in combination with a base, N(C2H5)3 or NaOAc. The coupling tends to produce a mixture of two isomeric alkenes, in which the newly formed bond is allylic or homoallylic to the ring juncture. 

The ax-membered spiro compound 210 reacts with H202/LiBr/HAc to form besides some byproducts the stereoisomeric 4-hydroxy-3 -bromopropyl-phosphinic esters 211 Z and E. This experiment of Stade strengthens the proposed mechanism for oxidative dealkylation formulated above. 

Rhodium (I)-phosphine systems lead to catalytic tetramerization. For example, the system [RhCl H with 1 to 2 moles of PPh3 is effective in the selective formation of an interesting spiro compound (XV) (152) free from other isomers. Although the detailed reaction path is unknown due to the inaccessibility of the intermediate complexes, the formation of (XV) may be visualized from a tetramer complex as follows ... 

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