91897-80-2Relevant articles and documents
New Synthetic Approach to Cyclopenta-Fused Heterocycles Based upon a Mild Nazarov Reaction
Occhiato, Ernesto G.,Prandi, Cristina,Ferrali, Alessandro,Guarna, Antonio,Venturello, Paolo
, p. 9728 - 9741 (2007/10/03)
The Pd-catalyzed coupling reaction of lactam or lactone-derived vinyl triflates and phosphates with α-alkoxydienylboronates gives conjugated alkoxytrienes in which one of the double bonds is embedded in a heterocyclic moiety. If subjected to mild acidic hydrolysis, these compounds undergo a 4π electrocyclization process (Nazarov reaction) which furnishes cyclopenta-fused O- and N-heterocycles in good yields. The scope of the work has been that of closely examining the role and effect of both the heteroatom and the heterocycle ring size on the outcome of the electrocyclization, as well as the torquoselectivity of this process. The presence of the heteroatom was essential in stabilizing the oxyallyl cation intermediate, thus allowing the reaction to occur. The ring size was also a basic parameter in the cyclization step: five-membered azacycles required more drastic conditions to give 5-5 fused systems and did so only after an initial hydrolysis to the corresponding divinyl ketones. As for the torquoselectivity, with both 2-methyl and 4-methyl substituted lactam derivatives steric interactions seem to have a role in forcing the conrotatory process to take place in one sense only: allowing the synthesis of diastereomerically pure compounds to be realized. Because different patterns of substitution on the heterocycle are compatible with the reaction conditions, the methodology developed could be very useful for the synthesis of natural products and biologically active compounds containing cyclopenta-fused O- and N-heterocycle moieties.
ACYLATION OF 1,3-BIS(TRIMETHYLSILYL)-PROPENE AND 1,8-BIS(TRIMETHYLSILYL)-1,7-OCTADIENE. OBTENTION OF (+/-)-1-ALKYL-2,5-DIVINYLCYCLOPENTANOLS.
Tubul, A.,Santelli, M.
, p. 3975 - 3982 (2007/10/02)
The addition of α,β-ethylenic acyl chlorides to 1,3-bis(trimethylsilyl)-propene 1 leads to propenyl-alkenyl ketones 7, while addition of acyl chlorides with 1,8-bis(trimethylsilyl)-1,7-octadiene 2 gives 1-alkyl-2,5-divinylcyclopentanols 10 and 1-acyl-2-trimethylsilylmethyl-3-vinylcyclopentanes 12 and 13.
PALLADIUM-CATALYZED CROSS-COUPLING OF VINYL IODIDES WITH ORGANOSTANNANES: SYNTHESIS OF UNSYMMETRICAL DIVINYL KETONES.
Goure,Wright,Davis,Labadie,Stille
, p. 6417 - 6422 (2007/10/18)
The palladium-catalyzed cross-coupling reaction of vinyl iodides with trimethyl- or tributylvinylstannanes in the presence of carbon monoxide gives unsymmetrical divinyl ketones in good yields. The reaction conditions are neutral and mild enough (40-50 degree C, 15-50 psig carbon monoxide) that other functional groups in either coupling partner can be brought unaltered into the coupled product. The E geometry in both partners is retained in the coupling product, and the Z geometry in the vinyltin reagent is maintained during the coupling reaction, but the coupled product undergoes slow Z to E isomerization under the usual reaction conditions. Isomerization of the divinyl ketone in the reaction medium is slowed in the dark. The reaction rate is especially sensitive to substituents on the vinyltin reagent, probably as a result of steric hindrance in the transmetalation step of the catalytic cycle.
