Ketals 2-acylation

Asymmetric reductions of a-fiinctionalized ketones, such as a-hydroxy ketones, a-halo ketones, a-sulfonoxy ketones, 1,2-diketones, a-keto acetals or thio ketals, acyl cyanides and a-amino or imino ketones with boron-based chiral reducing agents in a stoichiometric or catalytic manner have been reviewed. The oxazaborolidine-catalyzed borane reduction of protected a-hydroxy ketones, a-keto acetals and a-sulfonoxy ketones has been discussed in more detail. 

The primary and secondary alcohol functionahties have different reactivities, as exemplified by the slower reaction rate for secondary hydroxyls in the formation of esters from acids and alcohols (8). 1,2-Propylene glycol undergoes most of the typical alcohol reactions, such as reaction with a free acid, acyl hahde, or acid anhydride to form an ester reaction with alkaU metal hydroxide to form metal salts and reaction with aldehydes or ketones to form acetals and ketals (9,10). The most important commercial appHcation of propylene glycol is in the manufacture of polyesters by reaction with a dibasic or polybasic acid. 

The signal molecule, 30,C6-HSL and number of its analogues, with variations in the acyl chain and the hetero-ring, have been prepared [15,56,57] to investigate the mechanism of induction of carbapenem and luminescence in Erwinia carotovora and V.fischeri respectively. Essentially, the acylation of l-HSL with 3-oxoalkanoic acid by the same method as outlined for the preparation of AT-acyl-L-HSL delivers the desired derivatives. However, as the p-keto acids are thermally labile, these were prepared from the corresponding p-keto ester after the initial protection of the p-keto function as ethylene glycol ketal (route a, Scheme 6). 

A triketone is also an intermediate in a synthesis of 6-methyI-4-oxopyran-2-carboxylic acid from pentane-2,3-dione in which one carbonyl group is initially protected as the ketal (67JOC4105). Acylation by ethyl oxalate is accomplished under basic conditions, and ring closure and hydrolysis of the ketal are effected with acid. 

Dichloro-2,2-difluoroethylene, 105 (Diethylamino)sulfur trifluoride, 110 Reduction reactions (see also Deoxygenation, Reductive. . . ) of acetals and ketals Dibromoalane, 237 Diisobutylaluminum hydride, 237 Triethylsilane-Tin(IV) chloride, 237 of acetates and other esters to alkanes Nickel boride, 197 Triphenylsilane, 334 of acyl halides to alcohols Sodium cyanoborohydride-Tin(II) chloride, 280... 

Conjugate addition of acyl groups to naphthoquinones (3, 211).2 The acyl nickel carbonylate anion (1) undergoes conjugate addition to the ethylene ketal 2 to form a lithium adduct that can be trapped by allyl iodide to give 3 in 81% yield. This product can be converted in a few steps to the hydroxyquinone 4, a precursor of the naphthoquinone antibiotic deoxyfrenolicin (5). 

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