Phospholene

The only notable success to date in the use of (salen)metal systems in catalysis of asymmetric cyanide addition to epoxides was achieved by Pietrusiewicz, who reported the aluminium-catalyzed desymmetrization of phospholene meso-epoxide (Scheme 7.23) in moderate ee [47]. Despite these significant efforts, a truly prac-... 

Phi = NTs ([N-(p-toluenesulfonyl)iminio]phe-nyliodinane) 79 phomactin A 307 (+)-phonomactin 277 ( )-phoracantholide 299 phosphazene base 3 f. phosphazine base 31 phospholene epoxide 243 phosphoramidite 261 phosphoramidite ligand 247 piperidinephosphonate 103 pipermethystine 302 P K 177... 

The phosphetans (51) react with one equivalent of chlorine to give but-3-enylhalogenophosphines, which can be cyclized by heating or by treatment with halogen or aluminium chloride to the A -phospholen... 

Thermal decomposition of 1-methyl-A -phospholen in toluene at 356-444 °C yielded butadiene as the primary product. The activation parameters are in agreement with a mechanism involving ring opening to a biradical followed by fragmentation into butadiene, phosphorus, and methyl radicals. ... 

I-Phenyl-A -phospholen-l-oxide (126) and /rani -l,4-diacetoxybutadiene gave (127), which could be converted to the phosphole oxide. Reduction... 

The pyruvaldehyde and phenylglyoxal adducts (19) with trimethyl phosphite reacted with isocyanates to give the carbamoyl-1,3,2-dioxa-phospholens (20), probably as shown. These, with hydrogen chloride, gave phosphate esters of )3-keto-a-hydroxyamides. 

Biphilic Reactions with Dienes or Carbonyl Compounds. Stereochemical details have appeared of the reactions between substituted 1,3-dienes and halogenophosphines, such as dichloromethylphosphine (21a) and dibromo-phenylphosphine (21b). In general, both cis- and /ra/i5-adducts are formed, and they are not interconvertible via quinquecovalent intermediates. The conversion of these adducts to A -phospholens or to A -phospholen-l-oxides produces cis-trans mixtures. 

C. Reactions not involving P=0 or P=S Groups.—Enamine phosphine oxides (45) have been prepared by the addition of amines to 1-alkynyl-phosphine oxides, and the reactions of their anions with various electrophiles have been reported. - With ketones a Wittig-type reaction leads to the formation of a/3-unsaturated ketones, in 53—70% yield, while with epoxides cyclopropyl ketimines are formed. A Diels-Alder reaction of l-phenyl-A -phospholen-l-oxide (46) with 1,4-diacetoxybutadiene has been used in the preparation of l-phenyl-benzo[/>]phosphole (47), as... 

The reverse mesomeric effect (p -p conjugation) is believed to be very favourable in the A -phospholen system (5). Compared with the corresponding A -phospholens (6), the conjugated system (5) shows both Y and the phosphorus atom to be deshielded, and the vinyl proton is shielded. The cyclic nature of the molecule is important because the analogous... 

Definitive evidence on the role of heteroelements in the regjochemical control of the hydrozirconation may be exemplified with the reaction of phospholene-1 (7) with 1. The gem-phosphazirconocene compound 8 is selectively formed with P-coor-dination on the metal fragment. The ]3-zirconated product 10 was prepared with 1... 

Two series of phosphoranes (86 or 87) containing a dioxaphos-pholene ring and a 2-phospholene or 3-phospholene ring have been synthesised from trico-ordinate phospholenes (83) or (84) and 1,2-dicarbonyl compounds (85)1 7. The compounds were characterised by analysis, XH and J1P n.m.r. and, in contrast to earlier work,1 8 were found to be stable towards the retrodiene fragmentation. 

Phosphinic acids in the 3-phospholene series are converted into... 

In contrast with the behaviour of typical vinylphosphonic acid derivatives, the carbon-carbon double bond in the 1,2-oxa-phospholene (167) is remarkably unreactive towards a broad spectrum of reagents including electrophiles, most epoxidizing and organometallic reagents, as well as to dipolar addition reactants. Exceptional reagents are, however, N-bromoacetamide (NBA), ozone, dimethyllithiumcuprate, and sodium-naphthalene. 

Assignments. - Electric modulation of vibrational rotational bands of polar molecules included a study of phosphine.120 Ringbending (puckering) transition frequencies have been measured for the phospholene (42) for the ground and excited states.121 The PD deformation band for the sulphide (43) has been assigned.122... 

A less efficient method for the preparation of phospholes involves the bromination of phospholene oxides (5), the deoxygenation of the dibromophospholane oxides (6) so obtained with trichlorosilane, and finally dehydrobromination of dibro-mophospholanes 7 (Scheme 3) [30, 31]. 

Preparation of l-ethoxy-2-phenyl-4,5-dimethoxycarbonyl-A2- 5-phospholene 1-oxide — Reaction of a vinylicphos-phonite diester with an unsaturated carboxylate ester... 

A mixture of diethyl 2-bromo-l-phenylethenylphosphonite (30.3 g, 0.1 mol) and dimethyl maleate (14.4 g, 0.1 mol) was stirred for 4 h at room temperature under an argon atmosphere. At this time, hexane was added to the reaction mixture sufficient for complete precipitation, and the resultant crystals (unreacted dimethyl maleate) were removed by filtration. The oily residue was treated on a silica gel column (40/100 pm) using a pentane/acetone (8 2) mixture, allowing the elution and isolation after evaporation of pure l-ethoxy-2-phenyl-4,5-dimetho x yea rb o n y I - A2-X5-phospholene 1-oxide (8.9 g, 27%), which exhibited spectra and analytical data in accord with the proposed structure. 

The A3-phospholen sulphides (44), bearing reactive functional groups, may be reduced to the phosphine using nickelocene in the presence of allyl iodide.37 The intermediate nickel complex is decomposed with cyanide to free the functionalized A3-phospholen (45). 

The reaction of the phospholen (65) with aromatic acid chlorides in the presence of triethylamine, followed by addition of DaO, gives a ready route to aromatic [1-2H]-aldehydes with 100% incorporation of deuterium.55... 

Biphilic Reactions.—A most thorough investigation into the cycloaddition of buta-1,3-diene with dichloro(methyl)phosphine (30) has revealed some of the factors which influence the composition of the final products.32 Thus the A3-phospholen 1-oxide (31) is the product of the cycloaddition at room temperature, but at 90 °C the isomeric A2-phospholen 1-oxide (32) predominates after work-up. The yields of (31) and (32) are improved by a new work-up involving methanolysis rather than hydrolysis of the intermediate salts.32... 

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