Pyrone phosphonate

The convergent total synthesis of the mytotoxic (+)-asteltoxin was accomplished by J.K. Cha et al. The coupling of the two main fragments was achieved by the HWE olefinatlon of a jb/s(tetrahydrofuran) aldehyde with an a-pyrone phosphonate. The b/s(tetrahydrofuran) aldehyde was prepared by the Swern oxidation of the corresponding b/s(tetrahydrofuran) primary alcohol. Interestingly, under the oxidation conditions there was no epimerization of the a-stereocenter, but during the HWE olefinatlon a small amount of C8 epimer was formed. 

Industrially, a selectivity to DAA of between 90—95% can be achieved (64). The principal by-products are mesityl oxide and acetone trimers. j W-Triacetone dialcohol [3682-91-5] can form by condensation of acetone with diacetone alcohol (116). Dehydration of ry/ -triacetone dialcohol can yield semiphorone [5857-71-6] (6-hydroxy-2,6-dimethyl-2-hepten-4-one), which may in turn ring close to form 2,2,6,6-tetramethyl-y-pyrone [1197-66-6/, or ultimately dehydrate to phorone [504-20-1] (2,6-dimethyl-2,5-heptadien-4-one) (146). Similarly, an unsymmetrical acetone trimer can also be formed which dehydrates to 2,4-dimethyl-2,4-heptadiene-6-one. These impurities complicate the high purity recovery of DAA, and are thought to be responsible for a yellow discoloration of DAA. The addition of dibasic acid (147) or nitrogen containing carboxylic or phosphonic acids (148) has been patented as refined product stabilizing agents. 

Recently we have developed a more general approach to molecules exemplified by III. Thus the Diels-Alder cycloaddition of alkyne II and ct-pyrone, followed by aromatization by loss of carbon dioxide, led to the isolation of III (72%) (5). Alkyne II was obtained in high yields, in two steps from dichloroacetylene and triethylphosphite via Arbuzov-type reactions (5). Since the intermediate chloroalkyne phosphonate I was isolable (90%), phosphorus nucleophiles other than triethylphosphite could be used to give unsymmetrical alkyne diphosphoryl species. We have demonstrated this approach by the reaction of I with PhaPOEt and PhP(OEt)2 (5). 

Pyron. [Chemonic Industries] Bromi-nated phosphonated amines and nitrogen phosphwus salts flame retardants for textiles. 

Similarly, l,2-phenylenebis(phosphonic acid dimethyl ester) derivatives have been obtained from differently substituted 2-pyrones and l,2-bis(phosphonic acid dimethyl ester)acetylene as the reaction partners (Scheme 16.35) [38]. 

---