Synthesis from ketenes

III. SYNTHESIS FROM KETENES, ISOCYANATES AND ACYL HALIDES A. Ketenes... 

The ester of quinine (5) is an excellent catalyst for p-lactone synthesis from ketene and certain aldehydes. ... 

P-Hydroxy acids lose water, especially in the presence of an acid catalyst, to give a,P-unsaturated acids, and frequendy P,y-unsaturated acids. P-Hydroxy acids do not form lactones readily because of the difficulty of four-membered ring formation. The simplest P-lactone, P-propiolactone, can be made from ketene and formaldehyde in the presence of methyl borate but not from P-hydroxypropionic acid. P-Propiolactone [57-57-8] is a usehil intermediate for organic synthesis but caution should be exercised when handling this lactone because it is a known carcinogen. 

Wiskur SL, Fu GC (2005) Catalytic asymmetric synthesis of esters from ketenes. J Am Chem Soc 127 6176-6177... 

General procedure for the synthesis of a-bromovinyl tellurides from ketene stannyl (telluro) acetals To a solution of the appropriate ketene stannyl(telluro) acetal (1.0 mmol) in CH2CI2 (10 mL) cooled at -78°C (at 0°C for 5 h) was added dropwise a solution of NBS (0.445 g, 2.5 mmol) in CH2CI2 (25 mL). Th reaction mixture was stirred for 6 and 12 h (R=H). It was transferred to an Erlenmeyer flask and treated with a solution... 

Figure 2. Synthesis of orthoesters from ketene acetals and diols.

Lastly, Corey has developed B LA species 65, derived from zwitterionic oxazaboro-lidine 64 and tri-n-butyltin trifalte, as a novel catalybc system for the enanboselec-bve synthesis of P-lactones from ketene and aldehydes (Scheme 5.81) [152]. The reaction of B LA 65 with ketene generates intermediate A. The subsequent addition of the ketene acetal unit to the coordinated aldehyde (intermediate B) followed by extrusion of the P-lactone completes the catalybc cycle. 

Chiral fi-lactams. The synthesis of /5-lactams from ketene silyl acetals and Schiff bases (8, 484-485) results in asymmetric induction at C4 in the range 44 78% when optically active Schiff bases are used. An example is shown in equation (l)-... 

To avoid destructive side reactions, cyclopropanones have to be prepared at low temperatures in the absence of nucleophiles. A good example is the synthesis of cyclopropanone itself from ketene and diazomethane (see Section 16-4 A) ... 

Scheme 1.3 Pracejus enantioselective ester synthesis from phenyl methyl ketene.

Acrolein and condensable by-products, mainly acrylic acid plus some acetic acid and acetaldehyde, are separated from nitrogen and carbon oxides in a water absorber. However in most industrial plants the product is not isolated for sale, but instead the acrolein-rich effluent is transferred to a second-stage reactor for oxidation to acrylic acid. In fact the volume of acrylic acid production ca. 4.2 Mt/a worldwide) is an order of magnitude larger than that of commercial acrolein. The propylene oxidation has supplanted earlier acrylic acid processes based on other feedstocks, such as the Reppe synthesis from acetylene, the ketene process from acetic acid and formaldehyde, or the hydrolysis of acrylonitrile or of ethylene cyanohydrin (from ethylene oxide). In addition to the (preferred) stepwise process, via acrolein (Equation 30), a... 

In Section IV.D we describe the synthesis of complexes containing the dianionic enolato -C,0-ketenido ligand, which usually are not prepared from ketenes. In this section we will show how ketenes are useful reagents to prepare other enolato complexes. In most cases a ketene RR C=C=0 inserts into a M—C bond of a [M]—R" complex to give... 

The principal method of synthesis of the 1-oxides is the cycloaddition of A-sulfinylsulfonamides, for example, 417, to vinyl ethers." " " " N-phenyl-dimethylketimine" " (correction of an earlier " "" proposed structure), and A-sulfinylamines, for example, 418," ° to ketenes" " " " or alkenes." The adducts obtained from ketene itself are unstable above — 78°750,754,755a Pfeatment... 

C-aryl glycosides, 528 C-glycosides, 528 C-glycoside synthesis, 505 fronj enol ethers, 505 by free-radical methods, 507 from ketene acetals, 505 from malonate anion, 505 from 2-pyridylthio glycosides, 385... 

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