RESUMEN
A convergent, nine-step (LLS), enantioselective synthesis of α-cyclopiazonic acid and related natural products is reported. The route features a)â an enantioselective aziridination of an imine with a chiral sulfur ylide; b)â a bioinspired (3+2)-cycloaddition of the aziridine onto an alkene; and c)â installation of the acetyltetramic acid by an unprecedented tandem carbonylative lactamization/N-O cleavage of a bromoisoxazole.
RESUMEN
A one-pot three-component protocol for the preparation of arylsulfonyl alkynes through the reaction of ethynyl-benziodoxolone (EBX) reagents, DABSO (DABCO·SO2), and either organomagnesium reagents or aryl iodides with a palladium catalyst is reported. A broad range of aryl and heteroarylalkynyl sulfones were obtained in 46-85% overall yield.
Asunto(s)
Alquinos/síntesis química , Sulfonas/síntesis química , Alquinos/química , Catálisis , Indicadores y Reactivos , Estructura Molecular , Paladio/química , Sulfonas/químicaRESUMEN
Highly efficient protocols for the alkynylation of H-phosphi(na)tes and secondary phosphine oxides with silyl, aryl and alkyl ethynyl-benziodoxolone (EBX) reagents are reported. Alkynyl phosphorus compounds were obtained in 69-93% yield without the need for a transition metal catalyst at room temperature under open flask conditions.
Asunto(s)
Alquinos/química , Yodobenzoatos/química , Óxidos/química , Fosfinas/química , Ácidos Fosfínicos/química , Catálisis , Indicadores y Reactivos , Yodobencenos , Temperatura , Elementos de Transición/químicaRESUMEN
3-Methyl vinyl aziridine undergoes a mild MgI2-promoted S(N)2' ring opening and concomitant cyclization with fumarate Michael acceptors to give trisubstituted pyrrolidines. The process is efficient and highly diastereoselective. This methodology has been applied to a concise asymmetric synthesis of (+)-allo-kainic acid.
Asunto(s)
Aleaciones/síntesis química , Aziridinas/química , Ácido Kaínico/síntesis química , Pirrolidinas/química , Compuestos de Vinilo/química , Aleaciones/química , Ciclización , Reacción de Cicloadición , Ácido Kaínico/química , Estructura Molecular , EstereoisomerismoRESUMEN
The chiral sulfide, isothiocineole, has been synthesized in one step from elemental sulfur, γ-terpinene, and limonene in 61% yield. A mechanism involving radical intermediates for this reaction is proposed based on experimental evidence. The application of isothiocineole to the asymmetric epoxidation of aldehydes and the aziridination of imines is described. Excellent enantioselectivities and diastereoselectivities have been obtained over a wide range of aromatic, aliphatic, and α,ß-unsaturated aldehydes using simple protocols. In aziridinations, excellent enantioselectivities and good diastereoselectivities were obtained for a wide range of imines. Mechanistic models have been put forward to rationalize the high selectivities observed, which should enable the sulfide to be used with confidence in synthesis. In epoxidations, the degree of reversibility in betaine formation dominates both the diastereoselectivity and the enantioselectivity. Appropriate tuning of reaction conditions based on understanding the reaction mechanism enables high selectivities to be obtained in most cases. In aziridinations, betaine formation is nonreversible with semistabilized ylides and diastereoselectivities are determined in the betaine forming step and are more variable as a result.
RESUMEN
2-Vinylaziridines undergo a mild Pd-catalyzed ring-opening cyclization reaction with an ambient atmosphere of carbon dioxide to give 5-vinyloxazolidinones. The process is high yielding as well as regio- and stereoselective.