ABSTRACT
A chromium-mediated novel synthesis of carbohydrate-derived di- and trisubstituted (E)-α,ß-unsaturated esters or amides from a range of dichloroesters or amides and a variety of sugar aldehydes is reported. The process took place with total stereoselectivity and in high yields. A mechanism based on a sequential chromium-promoted aldol-type reaction and a completely stereoselective ß-elimination reaction is proposed to explain these results.
Subject(s)
Amides/chemical synthesis , Carbohydrates/chemistry , Chromium/chemistry , Esters/chemical synthesis , Amides/chemistry , Esters/chemistry , Molecular Structure , StereoisomerismABSTRACT
An efficient chromium-promoted alkyl- or silylcyclopropanation of alpha,beta-unsaturated amides is described. These reactions can be carried out on (E)- or (Z)-alpha,beta-enamides in which the C-C double bond is di-, or trisubstituted. This process takes place with total stereospecificity and the new stereogenic center is generated with high or total stereoselectivity. Some synthetic applications of the obtained silylcyclopropyl amides are also reported. Two mechanisms based on the generation of carbenoid or carbene complexes have been proposed to explain this cyclopropanation reaction.
Subject(s)
Amides/chemistry , Chlorides/chemistry , Chromium Compounds/chemistry , Cyclopropanes/chemical synthesis , Silanes/chemical synthesis , Amides/chemical synthesis , Cyclization , Cyclopropanes/chemistry , Molecular Structure , Silanes/chemistry , StereoisomerismABSTRACT
A novel chromium-promoted alkyl- and silyl cyclopropanation of (E)- or (Z)-alpha,beta-unsaturated amides in which the C-C double bond is di-, or trisubstituted is described. This process takes place with total stereospecificity, and the new stereogenic center is generated with high or total stereoselectivity. A mechanism is proposed to explain the cyclopropanation reaction.
Subject(s)
Amides/chemistry , Chlorides/chemistry , Chromium Compounds/chemistry , Cyclopropanes/chemistry , Silanes/chemistry , Catalysis , Molecular Structure , StereoisomerismABSTRACT
We describe herein a CrCl(2)-promoted cyclopropanation of alpha,beta-unsaturated amides. This reaction can be carried out on (E)- or (Z)-alpha,beta-enamides in which the C-C double bond is di-, tri-, or tetrasubstituted. In all cases the process is completely stereospecific and only a single diastereoisomer is obtained. In addition, cyclopropyl ketones were readily prepared by reaction of the cyclopropanecarboxamides (derived from morpholine) obtained with a range of organolithium compounds. A mechanism has been proposed to explain the cyclopropanation reaction.
