Intramolecular addition of vinyl and aryl radicals to oxime ethers in the synthesis of five-, six- and seven-membered ring systems

Abstract

The oxime ethers 2a-e have been cyclised with Bu,SnH to the alkoxyamino-3-methylidenechromanes 3a-e. Seven-membered ring formation was observed when the oxime ethers 7a. b were converted into the dibenzo[b,e]oxepines 8a. b under similar conditions. 1 -Methoxyaminoindanes 12a. b were produced from the cyclisation of the substrates I l a , b and the cis-fused cyclic products 15a, b and 18 were obtained from compounds 14a. b and 17, respectively.The construction of carbocyclic rings using intramolecular radical cyclisation has become a common strategy in organic synthesis. The first example of the intramolecular trapping of a radical by an oxime ether was reported by Corey and Pyne in 1983.2 The particular advantage of using an oxime ether seems to ! i F in the extra stability of the alkoxy aminyl radicalPaper 410289 1 K

Control of Asymmetry in the Radical Addition Approach to Chiral Amine Synthesis

“…At that time, oxime ethers were the most commonly explored C=N radical acceptors. [22,23,24] We considered that linking an amino or amido substituent to the C=N nitrogen atom could afford the same reactivity enhancement seen in oxime ethers, and would also provide opportunities for superior rotamer control needed for stereoselectivity. Both activation and stereocontrol would be achieved through one removable N -substituent on the imine, and the substituents on the carbon of the C=N bond would then be freed from those roles, offering potential for broader scope.…”

Asymmetric Methods for Radical Addition to Imino Compounds

“…Stereocontrol has been imparted through the substituent on the imino carbon, as exemplified by camphorsultam 4 (Figure 2.2b). Attempts to use chiral O-substituents on oximes for stereocontrol have been ineffective, presumably due to poor rotamer control [8,9].…”

Radical Addition-Initiated Domino Reactions of Conjugated Oxime Ethers

“…10,11) Although conjugated imines have been used as electrophiles and nucleophiles in inter-and intramolecular addition reactions, as well as heterodienes in cycloaddition reactions, reports pertaining to the use of conjugated imines in radical reactions are few. 12) It was envisioned that the versatility of conjugated imines would allow them to be used as substrates in radial-mediated domino reactions. Of the various different types of conjugated imine available, we selected conjugated oxime ether.…”