Pentachloride stereochemistry

The stereochemistry of the addition of phosphorus pentachloride to isolated acetylenes in non-polar solvents has been shown by n.m.r. to be CIS, as illustrated for the adduct (46) from propyne. This observation has been explained in terms of a four-centre process. Contrary to a previous report, the reaction of triphenylphosphine hydrobromide with phenyl-acetylene carboxylic acid (47) yields both the trans- and the known c/5-adducts. 

The structure XXII for rhynehophylline has been confirmed, and the relative stereochemistry at C-15 and C-20 has been elucidated, by a total synthesis (80) of (+) JV-methylrhynchophyllane (XXVI) (Marion s N-methylisorhynchophyllane), which had been prepared earlier by methyl-ation of (iso)rhynchophyllane with sodium methoxide and methyl iodide (28). The lactone (XXVII) of threo-3,4-diethyl-5-hydroxyvaleric acid was converted by reaction with phosphorus pentachloride into the corresponding S-chloroacid chloride (XXVIII), which on treatment with methylaniline gave the anilide XXIX. Reduction of XXIX with lithium aluminum hydride gave the aldehyde XXX, which slowly reacted with... 

The stereochemistry of chlorination of tran.v-stilbene with phosphorus pentachloride is dependent on the solvent system135. Anti addition is predominant in hexane, whereas syn addition is observed in dichloromethane. This observation is explained by two parallel reaction paths. 

N.Q.R. The C1 n.q.r. spectra of cyclic 1,3,2-/i -diazaphosphorines correlate with parameters estimated by CNDO/2 calculations. The structures of the intermediates produced in the reactions of formamides and acetamides with phosphorus pentachloride and phosphoryl trichloride have been studied by n.q.r. spectroscopy. The stereochemistry of dichlorodiazadiphosphetane has been studied, and evidence on the polarity of radial chloride atoms in chlorophosphoranes discussed. ... 

An early synthesis, published in 1983 and 1984 [83], requires three steps from 2-chloro-N-(2,4-dichlorophenyl)acetamide (Scheme 17.17). First, the amide group is transformed into imidoyl chloride with phosphorus pentachloride, followed by displacement of the two non-aromatic chlorine atoms by two equivalents of the potassium salt of 1,2,4-triazole. The triazolyl group borne by the imino bond being the best leaving group is replaced when reacted with a good nucleophile such as (4-chlorophenyl)methanethiol. The stereochemistry (E or Z) of the double bond is not stated in the literature. 

---