Phosphetanic acids

Phosphorinic, phospholanic, and phosphetanic acids are four-, five-, and six-membered phosphorus heterocycles, respectively, with a cyclic phosphinic... 

Scheme 1 Production of phospholanic and phosphetanic acids 1-3 via ethyl esters 4-6...

Phosphetanic acid can be prepared in low yield by reacting bromopropyl phosphonic dichloride with magnesium in ether (6.825). 

In preliminary studies, some of the bis-phosphetanes 71, 80, 81, and 82 have been tested in the hydrogenation of model dehydroamino acid derivatives. Selected results are given in Equation (14) <1999SL1975, 1999TL8365, 2004TA2169>. 

Yet further violations of the rule that phosphetans undergo substitution with retention of configuration have come to light. The phosphetan amides (111), normally resistant to hydrochloric, sulphuric, and trifluoroacetic acids, do, however, undergo methanolysis in the presence of BF3, when considerable inversion of configuration occurs at phosphorus. ... 

Hydrosilylation reactions are formal additions of Si-H units across multiple bonds. They are fundamental reactions in organosilicon chemistry. Despite early reports of Marinetti and Ricard on Pd-catalysed hydrosilylation of alkenes with phosphetanes (up to 65% ee with styrene) and of Zhang and co-workers on Ru-catalysed hydrosilylation of ketones (up to 54% ee with acetophenone), most of the work on enantioselective hydrosilylation with P-stereogenic ligands has been carried out with Rh(I) complexes and prochiral ketones as substrates. Initially, silyl ethers are formed but they are usually cleaved under acidic conditions affording alcohols. As a result, hydrosilylations of ketones are formally identical to hydrogenations but do not involve the manipulation of dihydrogen. The model substrate for enantioselective hydrosilylation is acetophenone (Scheme 7.17). 

The coupling of 3-tert-butyl [1 - " C]malonate (393) with the /3-amino acid derivative 395 to give amide 396 was developed as an alternative route to the 1,4 addition of 395 to the corresponding [l- " C]acrylate 394, which might have failed due to radiation-induced polymerization. Subsequent treatment with 2,4-bis(4-methoxyphenyl)-l,3,2,4-dithiadi-phosphetane-2,4-disulfide (Lawesson s reagent) followed by Raney nickel-mediated desulfurization of the thioamide function formed converted 396 into the target /3-amino acid ester 397. Intramolecular ester condensation upon treatment of 397 with sodium methoxide and concluding saponification and decarboxylation of the f-butyl ester function afforded the trisubstituted 4-[2- " C]piperidone derivative 398. 

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