Phosphorus, isomerization

The synthesis of vitamin Dj from a sensitive dienone was another etu-ly success of phosphorus ylide synthesis (H.H. Inhoffen, 1958 A). This Wittig reaction could be carried out without any isomerization of the diene. An excess of the ylide was needed presumably because the alkoxides formed from the hydroxy group in the educt removed some of the ylide. 

Quite recently, Ciampolini and coworkers have reported the synthesis of two isomeric mked oxygen-phosphorus macrocycles and the crystal structures of their cobalt complexes. Synthesis of macrocycle 27 was accomplished by condensation of 1,2-bis-(phenylphosphino)ethane dianion with 2,2 -dichlorodiethyl ether in THE. The two isomers of 27 were isolated in 1.5% and 2% yield. The synthesis is formulated in Eq. (6.17), below. 

Alkylation of these mercapto compounds in alkaline solution gives only the S-methyl derivatives. Of the four isomeric A-methyl derivatives, the 4-thioquinazolines, (28) and (29), have been obtained from the corresponding oxo compounds with phosphorus pentasulfide but the corresponding 2-thio derivatives (30) and (31) are not known. However, derivatives of substance (31) with methyl replaced by... 

Two isomeric alcohols, known as vetivenol, also exist in the oil. By treatment with phosphorus pentachloride this mixture of alcohols is converted into a chloride, or mixture of chlorides, which on reduction yields an artificial vetivene, having the following characters —... 

Photolyses of 3-substituted phenyl azides 53 in hot diethylamine containing pyrene, a singlet sensitizer, furnish mixtures of the 4- and 6-substituted 3ff-azepines 54 and 55. The isomers, however, were not separated and the yields were based on quantitative GC analysis of the reaction mixtures.176 Of mechanistic significance is that the ratios of the isomeric azepines obtained compare favorably with those observed in the deoxygenation of 3-nitroarenes with trivalent phosphorus compounds. 

The deoxygeneration of nitroarenes by trivalent phosphorus compounds in the presence of amines is a useful route to 3/f-azepin-2-amines (cf. compounds 32, Section 3.1.1.4.2.2.). Subsequently, it has been shown, by carrying out the reaction in strongly basic solution, that the process can be extended to the synthesis of 1H-. 3H- and 5//-2-benzazepines from nitronaph-thalenes 43 For example, 1-nitronaphthalenes 3 with dimethyl phosphite in the presence of sodium methoxide and a primary or secondary aliphatic amine, yield the dimethyl 5//-2-ben-zazepin-3-yl phosphonates 4 accompanied, in some cases, by the isomeric 3//-2-bcnzazepin-3-yl phosphonates 5. 

The six isomeric tris(methylthienyl)phosphines, e.g. (2), have been prepared by the reaction of methylthienyl-lithium derivatives with phosphorus tribromide. ... 

Surface-mediated addition of HC1 or HBr can be carried out in the presence of silica or alumina.150 The hydrogen halides can be generated from thionyl chloride, oxalyl chloride, oxalyl bromide, phosphorus tribromide, or acetyl bromide. The kinetic products from HC1 and 1-phenylpropyne result from syn addition, but isomerization to the more stable Z-isomer occurs upon continued exposure to the acidic conditions. 

The migrating group retains its configuration. Some reaction conditions can lead to syn-anti isomerization at a rate exceeding rearrangement, and when this occurs, a mixture of products is formed. The reagents that have been found least likely to cause competing isomerization are phosphorus pentachloride and p-toluenesulfonyl chloride.283... 

---