Direct, regioselective synthesis of 2,2-dimethyl-2H-chromenes. Total syntheses of octandrenolone and precocenes I and II

Herein is reported an efficient method for the synthesis of 2,2-dimethyl-2H-chromenes in a single step from the corresponding phenol and 3-methyl-2-butenal via microwave irradiation in CDCl₃. This protocol features a mild reaction environment (neutral, no added catalyst) which yields regioselective formation of the chromene and displays tolerance toward acid- and base-sensitive protecting groups.     

Direct preparation of 3,4-dichloro-2,-dimethyl-3-chromenes from 2,2-dimethyl-4-chromanones

Reaction of 2,2-dimethyl-4-chromanones($\text{1}$) with two equivalents of phosphorus pentachloride affords, 3,4-dichloro-2,2-dimethyl-3-chromenes($\text{2}$) in variable yields depending on the substituents of the aromatic ring. A plausible pathway for this reaction is given.     

An efficient synthesis of 4-chromanones

A two step efficient and practical synthesis of a variety of 4-chromanones is described. Phenols undergo a Michael addition to acrylonitriles in the presence of catalytic amounts of potassium carbonate and tert-butanol to generate the corresponding 3-aryloxypropanenitriles in 50-93% yields. Treatment of the resulting aryloxypropionitriles with 1.5 equiv of TfOH and 5 equiv of TFA, followed by an aqueous work up afforded 4-chromanones in moderate to excellent yields.     

Organocatalyzed Kabbe condensation reaction for mild and expeditious synthesis of 2,2-dialkyl and 2-spiro-4-chromanones

An expeditious Kabbe condensation reaction for the synthesis of 2,2-dialkyl and 2-spiro-chroman-4(1H)-ones has been developed using pyrrolidine-butanoic acid in DMSO as bifunctional organocatalyst. Unlike existing methods, this reaction proceeds at room temperature with high yields, rendering it an attractive method to synthesize a vast variety of privileged 4-chromones.     

A new synthesis of homoisoflavanones (3-benzyl-4-chromanones)

Two 7-hydroxyhomoisoflavanones ( / ) have been synthesized from corresponding 2'-hydroxydihydrochalcones ( / ) in about 33% overall yields. The stages are : (1) selective protection of C₄'-hydroxyl in ( / ) with EtO.CH₂Cl (1 molar equiv.) In the presence of dry K₂C0₃ and acetone at r.t.; (ii) reaction with one more molar equiv. of EtO.CH₂Cl at 60–70° without Isolating products ( / ) (iii) cyclizatlon of resulting α-hydroxymethyl derivatives ( / ) with 4% aq. aIc. Na₂C0₃ and (iv) deprotection of resulting 7-ethoxymethoxy homoisoflavanones ( / ) with 10% CH₃0H-HC1. The explanations for the formation of ( / ) and ( / ) are given.     

Efficient and regioselective synthesis of 2-alkyl-2H-indazoles

An efficient and regioselective synthesis of 2-methyl-2H-indazoles and 2-ethyl-2H-indazoles using trimethyloxonium tetrafluoroborate or triethyloxonium hexafluorophosphate is reported.     

A new pathway for the synthesis of 2,2-dimethyl-3,3-dichlorocyclopropanecarboxylic acid

Conclusions A new pathway has been proposed for the synthesis of 2,2-dimethyl-3,3-dichlorocyclopropanecarboxylic acid from dimethylvinylcarbinol.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 679–681, March, 1987.     

A novel synthesis and transformations of isothiochroman 2,2-dioxide

A convenient synthesis of isothiochromen-4-one 2,2-dioxide was carried out via cyclisation of o-cyanobenzyl thioacetate by a Thorpe reaction. The reactions of isothiochromen-4-one 2,2-dioxide with nitrogen-containing nucleophilic reagents have been investigated.     

The synthesis of certain 4-mono- and 4,7 dihydroxy-1,10-phenanthrolines

Aminocrotonates and cinnamates formed by the action of ethyl acetoacetate and ethyl benzoylacetate on substituted 8-aminoquinolines have been cyclized to 4-hydroxy and 4,7-dihydroxy-1,10-phenanthrolines.     

A concise and regioselective synthesis of 1-alkyl-4-imidazolecarboxylates

Reaction between ethyl 3-N,N-(dimethylamino)-2-isocyanoacrylate (1) and a primary amine (2) regioselectively affords 1-alkyl-4-imidazolecarboxylates (3) in good yields (52-89%). The method is applicable to unhindered and hindered amine substrates, as well as those containing reactive functionality such as alcohols and secondary and tertiary amines. [reaction: see text]     

Preparation and catalytic hydrogenation of 4,6-dimethyl- and 4,7-dimethyl-8-methoxycoumarins. A 4-methyldihydrocoumarin synthesis

Reduction of the title coumarins at 1500 psi and 150° over 10% palladium on charcoal provides a simple route to dihydrocoumarins and/or ethyl butanoates, hydrogenolysis products of the lactone. Lower pressures and temperatures tend to yield only the dihydrocoumarin. The butanoates are readily converted to the dihydrocoumarins in polyphosphoric acid.