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Mukaiyama and Torgov Chemistry in the Synthesis of (D-homo) Steroid Skeletons

Saraber F., Drach S., Baranovsky A., Charnikhova T., Pogrebnoi S., Jansen B., Groot A.

Polish Journal of Chemistry

2006

Vol. 80, nr 4

535-548

Three new, short, and efficient procedures have been developed for syntheses of steroid and D-homo steroid skeletons by application of Mukaiyama and Torgov chemistry. An important element in the first and in the second route is a Mukaiyama-Michael reaction with transfer of the silyl group from the starting silyl enol ether to the carbonyl group of the receiving enone. In this way a new silyl enol ether is obtained which enables either a selective reaction with the silyl enol ether in ring D as in route 1, or a selective reaction with the unprotected carbonyl group in ring B as in route 2. In all three approaches the C12-C13 bond is constructed using a Mukaiyama reaction of a Torgov type carbocation precursor with a silyl enol ether as the key transformation. In route 1, Zieglers triketone, which has been used before in the synthesis of 9,11-dehydroestrone methyl ether, has been prepared in four easy steps and in 70% overall yield, using the reactions mentioned above. In the second route a selective Grignard reaction of vinyl magnesium bromide with the unprotected carbonyl group of methoxy tetralone leads to a Torgov type intermediate. This can be converted easily into a carbocation, which then reacts intramolecularly with the silyl enol ether in ring D, under formation of the C12-C13 bond to complete the synthesis of cis (D-homo) steroid skeletons. In the third route, C17 substituted C,Dtrans coupled (D-homo) steroid skeletons have been prepared via an intermolecular addition of a carbocation, generated with ZnBr2 from a Torgov reagent, to a silyl enol ether containing ring D precursor. The adducts have been cyclized under formation of the C8-C14 bond by treatment with acid and the double bonds in the cyclized products have been reduced to all trans steroid skeletons. A chiral five membered silyl enol ether containing ring D precursor has been synthesized from carvone, and used as starting compound in the synthesis of a chiral C17 functionalized steroid.

Trialkylsilyl Triflates-Practical Diastereoselective Catalysts in Conjugate Addition Reaction of Silyl Ketene Acetals and alfa, beta-Unsaturated Ketones

Michalak K., Wicha J.

Polish Journal of Chemistry

2004

Vol. 78 / nr 2

205-215

Catalytic effect of trimethylsilyl triflate (TMSOTf) or tert-butyldimethylsilyl triflate (TBSOTf) in conjugate addition reaction of the respective trialkylsilyl derivatives of thioester enolates (silyl ketene acetals) 2a-2e and _,_-unsaturated ketones 1a-1c has been studied. It was shown that silyl triflates are efficient catalysts with stereochemical profile similar to that of trityl hexachloroantimonate. The use of silyl triflates is particularly advantageous in tandem reactions involving conjugate addition as the first step.

A convenient synthesis of alpha-substituted vinylphosphonates based on dithio- and selenophosphates

Maciągiewicz I., Dybowski P., Skowrońska A.

Polish Journal of Chemistry

1998

Vol. 72, nr 11

2389-2393

A convenient synthesis of alpha-substituted vinylphosphonates based on the reaction of readily available S-(beta-oxoalkyl)dithiophosphates and Se-(beta-oxoalkyl)selenophosphates with sodium dialkyl phosphites is described.