Enone

About: Enone is a research topic. Over the lifetime, 5683 publications have been published within this topic receiving 102109 citations.

Enantioselective Lewis acid catalysis of intramolecular enone [2+2] photocycloaddition reactions.

Abstract: Asymmetric catalysis of photochemical cycloadditions has been limited by the challenge of suppressing the unselective background reaction. Here, we report that the high cross-section ππ* transition of 5,6-dihydro-4-pyridones, a versatile class of enone substrates, undergoes a >50 nanometer (nm) bathochromic absorption shift upon Lewis acid coordination. Based on this observation, enantioselective intramolecular [2+2] photocycloaddition reactions (82 to 90% enantiomeric excess) were achieved with these substrates using 0.5 equivalents of a chiral Lewis acid upon irradiation at a wavelength of 366 nm. One of the products was applied as a key intermediate in the total synthesis of (+)-lupinine and the formal synthesis of (+)-thermopsine. Several enones show similar bathochromic shifts in the presence of a Lewis acid, indicating that chiral Lewis acid catalysis may be a general approach toward enantioselective enone [2+2] photocycloadditions.

Synthetic Applications of Intramolecular Enone-Olefin Photocycloadditions

Abstract: The intramolecular enonmlefin photocycloaddition, the light-induced [2+2] cycloaddition of a ground-state olefin tethered to an excited-state enone to form a cyclobutane, was first reported by Ciamician in 1908 when he observed the formation of carvone camphor on prolonged exposure of carvone to \"Italian sunlight\"' (Figure 1). Buchi's reinvestigation of this process confirmed the isomerization and sparked new interest in the reaction? The rapidity with which complex systems could be constructed by this method was recognized by Cookson3 who irradiated the Diels-Alder adduct of quinone and cyclopentadiene and by Eaton' who utilized a similar intramolecular photocycloaddition in his synthesis of cuhane. This reaction was first applied to the total synthesis of a natural product by Wiesner who prepared 12-epilycopodine utilizing an intramolecular photocycloaddition5 (Figure 2). Corey: Eaton,' and de May0,8.~ among others, subsequently began to investigate the intermolecular enone-olefin photocycloaddition, and these studies culminated in several successful synthetic applications, including the synthesis of caryophyllene'O and bourbonene,'l as well as a proposed mechanistic rationale for the reaction. While the major disadvantage of the intermolecular photocycloaddition is its low regioselectivity in some systems, this problem can be substantially overcome by incorporating the olefin and the enone in the same molecule. Although many of the early examples of the reaction were intramolecular, this variation saw only limited use until the late 1970s when its potential for the rapid construction of systems of

Studies in natural product chemistry

Abstract: The first section of this thesis is concerned with a biogenetic-type approach to the synthesis of the aconitine-lycoctonine group of diterpene alkaloids. The synthetic precursor, atisine, was transformed in an eleven step sequence into a keto-tosylate. This material underwent a novel, stereospecific pyrolytic rearrangement to give a key intermediate in the proposed atisane-aconane biogenesis, whose constitution and stereochemistry were confirmed by anx-ray crystallographic analysis, conducted on a heavy atom derivative. Our efforts to convert this intermediate into the desired aconitine-lycoctonine skeleton, a task which had already been accomplished in principle by other workers, met with limited success. N. M. R. studies on some acetamides, obtained in the foregoing synthesis, revealed an interesting example of restricted rotation around the bond. Variable temperature work enabled a crude barrier to rotation to be extracted. The second section of the thesis, also in the realm of diterpenes, concerns the synthesis of the cassane skeleton, in a biogenetically-patterned fashion, from isopimaric acid. The route from isopimaric acid to an important intermediate enone is described. Despite numerous attempts,we could not induce the Wagner-Meerwein rearrangement in this enone,which would have resulted in the desired cassane skeleton.