A novel synthesis of amino acid derivatives of phospholene oxides

A convenient synthetic approach is established to prepare a new class of 1-l-α-amino acid derivatives of phospholene oxides by amination of (±)-1-chloro-2-phospholene-1-oxides with several optically pure l-α-amino acid esters. All compounds obtained as a diastereomeric mixture in good to high yields. The two diastereomers were successfully separated by column chromatography and structurally identified by their spectral analyses.     

Preparation of 2-phospholene derivatives from zirconacyclopentenes

Zirconacyclopentenes, which are easily prepared from alkynes, alkenes, and zirconocene compounds, reacted with dichlorophenylphosphine to give 2-phospholene in high yields. The reaction was performed conveniently in one-pot from an alkyne, alkene, dichlorophosphine, and zirconocene compounds.     

Hydroformylation of styrene in the presence of platinum(II) complex catalysts incorporating cyclic phosphines and phosphonous diesters as P-ligands

The hydroformylation activity of various 5- and 6-membered P-heterocycles was investigated in platinum-catalysed hydroformylation of styrene. All of the tested ligands, such as the phosphole-, oxaphosphorine- and phoshinine-based ligands proved to be catalytically active. Especially good aldehyde selectivities were obtained with the chelating diphenylphosphino-tetrahydrophosphinine and diphenylphosphino-hexahydrophosphinine ligands. While the two aldehyde regioisomers were formed close to equimolar amounts with the monodentate ligands, high branched selectivities were observed with the chelating ones. The effect of the 4-substitution of the parent styrene on chemo- and regioselectivity was investigated.     

Alkylation and cyclopentannulation of phospholene derivatives

The deprotonation of 1-phenyl-3-phospholene 1-oxide, 1-sulfide or 1-borane with 1 or 2 equiv of LDA, followed by quenching with electrophiles gave a range of 2-mono- or 2,5-disubstituted phospholene derivatives in good yield. Only trans substitution in relation to the P-Ph group was observed. Treatment of lithiated phospholene intermediates with 1,3-dihaloalkanes afforded annulated 2-phenyl-2-phosphabicyclo[3.3.0]oct-3-ene derivatives. The annulation reactions occurred with high regio- and stereoselectivity and led to the exclusive formation of the exo-Ph-P substituted products.     

A novel preparation of chlorophospholenium chlorides and their application in the synthesis of phospholene boranes

A novel preparation of 1-chloro-3-methyl-3-phospholenium chlorides was developed by reacting 1-substituted-3-methyl-3-phospholene 1-oxides with oxalyl chloride. The obtained cyclic chlorophosphonium salts were reacted with LiBH₄ to afford the corresponding 1-substituted-3-methyl-3-phospholene boranes. The latter protocol involves a silane-free deoxygenation, and borane complex formation. In one instance, a 2-phospholene borane and the corresponding P-oxide were synthesized via rearrangement of the double bond in the cyclic chlorophosphonium salt. This double bond migration was investigated by quantum chemical calculations.