H. Ila

Cationic benzoannelation of active methylene ketones via oxoketendithioacetals

α-Oxoketendithioacetals are shown to be useful intermediates for benzoannelation of α-methylene ketones by reactions with allylmagnesium bromide followed by cationic cyclizations of the resulting carbinolacetals.

Attempted Simmons-Smith reaction on α-oxoketene dithioacetals: A new general route to 3,4-substituted and annelated thiophenes

Abstract A new general method for 3,4-substituted and annelated thiophenes through intramolecular cyclocondensation of a sulphonium ylid intermediate under Simmons-Smith reaction conditions on α-oxoketene dithioacetals has been reported.

Cyclocondensation of oxoketene dithioacetals with 3-aminopyrazoles: a facile highly regioselective general route to substituted and fused pyrazolo a]pyrimidines

Abstract Cyclocondensation of 3-aminopyrazole ( 1a ) and 3-amino-5-methylthio-4-phenylpyrazole ( 1b ) withα-oxoketene dithioacetals ( 2a - j derived from acyclic active methylene ketones affords 5-methylthio-6,7-substituted pyrazolo[1,5- a ]pyrimidines ( 3a - J ) exclusively. The reaction was found to be equally successful for the synthesis of 7-styryl,7-(4-aryl-1,3-butadienyl) and 7-(6-aryl-1,3,5-hexatrienyl)pyrazolopyrimidines ( 7a - f ) from the respective enoylketene dithioacetals ( 6a - f ). Similarly, the reaction of 1a and 1b with cyclic and benzocyclic ketene dithioacetals also afforded the angularly fused 5-methylthiopyrazolo pyrimidines regioselectively in good yields. However the oxoketene dithioacetal from cyclopentanone yielded both angularly and linearly fused regioisomers 10 and 11 respectively in nearly equal amounts. Some of the 5-methylthiopyrazolopyrimidines were dethiomethylated with Raney nickel to afford 5-unsubstituted derivatives in good yields.

Cycloaromatization of δ-oxoketendithioacetals with benzylmagnesium chloride: A novel naphthalene annelation reaction

δ-Oxoketendithioacetals derived from acyclic and cyclic ketones are shown to react with benzylmagnesium chloride to give novel naphthoannelated aromatic compounds by sequential 1,4- and 1,2-additions followed by subsequent cycloaromatization of the resulting carbinols.

Anionic [4+2] cycloaddition reactions of indole-2,3-dienolate with dienophiles: A facile regiospecific route to substituted carbazoles

Indole 2,3-dienolate derived by deprotonation of 1,2-dimethylindole-3-carboxaldehyde is shown to be useful 1,4-dipole synthon (anionic indolo-2,3-quinodimethane) which undergoes facile cycloaddition with wide range of dienophiles affording substituted carbazoles in highly regiospecific fashion.

Cycloaromatization of ∝-oxoketene dithioacetals with 3-methyl-5-lithiomethylisoxazole: A new general approach for synthesis of substituted and annelated 1,2-benzisoxazoles☆

Abstract A new general method for the synthesis of substituted and annelated 1,2-benzisoxazoles has been developed by cycloaromatization of ∝-oxoketene dithioacetals with 3-methyl-5-lithiomethylisoxazole.

Cycloaromatization of α-oxoketene dithioacetals and β-oxodithioacetals with benzyl-,1-(naphthylmethyl) and 2-(naphthylmethyl)magnesium halides: Synthesis of condensed polynuclear aromatic hydrocarbons

An efficient route for the synthesis of substituted naphthalenes, phenanthrenes and other polynuclear aromatic hydrocarbons has been developed. The methodology involves 1,2- (or sequential 1,4- and 1,2-) addition of either benzyl, 1-(naphthylmethyl) or 2-(naphthylmethyl) magnesium halides to α-oxoketene dithioacetals or β-oxodithioacetals followed by borontrifluoride etherate catalyzed cycloaromatization of the resulting carbinols.

Chloroallyl anion : Highly regio- and diastereoselective α-addition of chloroallyl zinc reagent to carbonyl compounds

The chloroallyl zinc reagent generated insitu by deprotonation of allyl chloride in the presence of lithium diisopropylamide and zinc chloride undergoes highly regio- and diastereoselective α-addition to carbonyl compounds to give syn chlorohydrins which on treatment with base afford cis vinyloxiranes in high yields.

Cyclocondensation of α-oxoketene dithioacetals with β-lithioamino-β- substituted acrylonitriles:synthesis of 2,6-substituted and 5,6-annelated 3-cyano-4- (methylthio) pyridines

Abstract The lithiated β-amino-β-substituted acrylonitriles 4a - d generated in situ by reaction of lithioacetonitrile with either acetonitrile or substituted nitriles undergo cyclocondensation with α-oxoketenedithioacetals through 1,4-addition to afford 2,6-substituted and 5,6-annelated-4-(methylthio)-3-cyanopyridines 6a - m , 11a - h and 12a - b in good yields. A few of the 2,6-diheterylpyridines 6n - q were also synthesized following this procedure. The corresponding α-cinnamoyl 12a - c and α-(5-aryl-2,4-pentadienoyl) ( 12d ) ketenedithioacetals on the other hand underwent cyclization with 4a to afford the corresponding 4-aryl- (or 4-styryl-6-[2-bis (methylthio)ethenyl]-3-cyanopyridines l4a - d in good yields. Raney Nickel desulphurization of some of these pyridines afforded products of reductive dethiomethylation and those formed by reductive alkylation of nitrile group.

Cycloaromatization of α-oxoketene dithioacetals with enaminone derived carbanions

Abstract Lithium enolates 3b and 6b derived from 1,3,6-trimethyluracil ( 3a ) and 3-pyrrolidinocrotonate ( 6a ) undergo regioselective γ-1,4- and γ-1,2-additions respectively with α-oxoketene dithioacetals 7 to yield the corresponding quinazolines and amino substituted aromatic compounds after subsequent cycloaromatization.