Acetone adducts

Six-membered heterocycles with two heteroatoms are prepared by reaction of diketene with a substrate containing a C—O or C—N multiple bond. With carbonyl compounds diketene reacts in the presence of acids to give l,3-dioxin-4-ones. The best known is 2,2,6-trimethyl-4H-l,3-dioxin-4-one [5394-63-8] (15), the so-called diketene—acetone adduct, often used as a diketene replacement that is safer to handle and to transport, albeit somewhat less reactive than diketene itself (103,104), forming acetylketene upon heating. 

A shippable but somewhat less reactive form of diketene is its acetone adduct, 2,2,6-trimethyl-4JT-l,3-dioxin-4-one (15) (103,104). Thermolysis of this safer to handle compound provides acetylketene, a reactive intermediate that can be used for acetoacetylation and cycloaddition reactions. The diketene—acetone adduct as weH as / fZ-butylaceto acetate [1694-31 -1] (also used for aceto acetylations by the trans aceto acetylation reaction) (130), are offered commercially. 

Dichlorothiophene 1,1-dioxide (168) is stable and of particular interest in the Diels-Alder reactions112. Thus, when 168 is treated with cyclopentadiene in acetone, adducts... 

The second and third steps in the monomer synthesis involve the replacement of bromine with an acetylene protected by an acetone adduct, followed by cleavage of the adduct. These steps will be discussed in more depth later as they are the same for systems containing only monomer or a monomer/oligomer mixture. 

The monomer/oligomer mixtures were used In the third step of the reaction sequence, the replacement of bromine with 2-methyl-3-butyn-2-ol by use of the bls(trlphenylphosphlne) palladium chloride catalyst system. This reaction used a trlethylamine/pyridine solvent system to replace the bromines on the ether sulfone with ethynyl groups protected by acetone adducts. The acetone protecting groups were then removed In a toluene/methanol/potasslum hydroxide solvent system. 

The intermediate acetone adduct is reddish in color and forms with a bimolecu-lar rate constant of 5 x 10 s This intermediate decomposes according... 

X-ray crystallography of PQQ [28], (PQQ)2(K) [28], and (PQQ)(Na)2 [29] has been reported. Coordination of the potassium ion involves the 7-carboxyl oxygens as well as the N(6) and 0(5) atoms. In the sodium complex, additional interactions with the 0(4) atom and the 2-carboxyl group are observed. As yet, crystalline preparations of PQQ-heavy metal complexes have not been obtained [28], X-ray crystallographic data of the PQQ acetone adduct [30] and the 2,4-dinitro-phenylhydrazone of PQQ triester [31 ] have also been presented. 

Substituted-l-benzotelluropyrylium salts react with dry acetone at room temperature to afford the corresponding acetone addition products 35 and 36 (Equation 9) <1999J(P1)1665>. The exocyclic unsaturated adduct 36 appears to form from acid-promoted dehydrogenation of the initially formed acetone adduct. 

The formaldehyde adduct (13a) was hydrolyzed and R-(—)-. 

Most of the solvent is removed by pumping at ambient temperature. Then cleavage of the salt-acetone adduct and removal of the remaining solvent are carried out at 100° while pumping for 2 hours. A —195° cold trap is placed on the vacuum line to allow collection of the volatile materials for reuse in preparing more salt. This procedure allows the salt to be coated on the walls of the vessel in a finely divided state as the volatile acetonitrile and hexafluoroacetone are removed. 

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