A-Ketoketenes

N-Sulfinylamines are useful N—S two-atom fragments and react readily with a-ketoketenes to give l,2,3-oxathiazin-4-one 2-oxides (77JCS(P1)904,79CB1012). Reaction with azoalkenes gives 1,2,3,6-thiatriazines (77S305) as shown in Scheme 23. 

The copper(I)-catalyzed addition of Grignard reagents to P-(alkylthio)-a,p-unsaturated esters is the preferred protocol for substitution of the alkylthio substituent, e.g. (310 - 311),21 while potassium enolates add to a-ketoketene dithioacetals, e.g. (312 — 313), without dialkylation (Scheme 96).218b,c Further, Hanessian reports an expedient synthesis of penam (315) via intramolecular cyclization of the (3-lactam nitroalkene (314), but loss of the methylthio moiety does not occur spontaneously (Scheme 97).219... 

Ketene A compound of the general type R R C=C=0. Where both R and R are alkyl groups it is more correctly called a ketoketene. See also aldoketene. 

It is reported that, at 75°C in the presence of a Lewis acid catalyst, 2,2,6-trimethyl-l,3-dioxin-4-one (17) undergoes fragmentation to give an a-ketoketene and acetone. In the presence of... 

Simple alcohols are known to attack a-ketoketenes, derived from dioxinones at elevated temperatures, to give the acetoacetylated products (Equation (11)), typically in excellent yields, as are more complex alcohols such as those derived from steroids and carbohydrates <85JOC2431>. 

Photosensitized oxygenation of a-ketoketene mercaptals has been described and these give dioxetanols, which subsequently collapse to carboxylic acids. Photo-oxidation of the mesoionic compounds (63) and (64) gives ring-cleavage products via endoperoxides and irradiation of tetrathiatetracene and of its selenium analogue in halocarbon solvents leads to radical cation salts. 

Without additional reagents C-Acylation with mercaptan elimination a-Ketoketene mercaptals from trithioorthocarboxylic acid esters... 

Bis(alkylthio)pyridines from a-ketoketene mercaptals via p-cyano-a-hydroxyketene mercaptals... 

Organolithium compds. [s.a. under Me2AlN(Me)Ph] 1,2-Addition to a-ketoketene mercaptals s. 44, 494... 

Acylene-1,1-dithiols a-Ketoketene mercaptals a- Dimercaptomethy leneketones 15... 

Carbonyl Compounds. In the case of aldehydes, only self-condensation products are obtained, whereas aliphatic ketones usually form the corresponding dithiocarboxylates or a-ketoketene dithioacetals. If cyclic ketones are used, occurrence of carbon-carbon cleavage or formation of a-ketoketene acetals depend on the steric demands of the base. Treatment of cyclohexanone with lithium 4-methyl-2,6-di-f-butylphenoxide (12) (readily obtained by treatment of the phenol with n-butyllithium) and CS2, followed by methylation, leads via the dithiocarboxylate ion (13) to the a-ketoketene dithioacetal (14) (eq 10). ... 

---