Solvent-controlled intramolecular [2 + 2] photocycloadditions of alpha-substituted enones.
The regio- and stereoselectivity of intramolecular [2 + 2] photocycloadditions of 2'-hydroxyenones are shown to be solvent-dependent. In the presence of aprotic solvents, 2'-hydroxyenones undergo photocycloadditions in a manner consistent with the presence of an intramolecular hydrogen bond between the carbonyl group and the tether's hydroxy functionality. In protic solvents, intermolecular interactions appear to disrupt the intramolecular hydrogen bond, providing products with complementary diastereoselectivity. If the facial accessibility of the alpha-tethered olefin is limited, the cycloadditions proceed to give head-to-tail or head-to-head regioisomers, depending on the nature of the solvent employed.
Ng
Stephanie M
SM
Department of Chemistry, Merkert Chemistry Center, Boston College, 2609 Beacon Street, Chestnut Hill, Massachusetts 02467, USA.
Bader
Scott J
SJ
Snapper
Marc L
ML
D000475:Alkenes / Q000737:chemistry*; D003500:Cyclization; D003503:Cyclobutanes / Q000737:chemistry; D006860:Hydrogen Bonding; D007659:Ketones / Q000737:chemistry*; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010777:Photochemistry; D012997:Solvents / Q000737:chemistry*; D013237:Stereoisomerism
D000475:Alkenes; D003503:Cyclobutanes; D007659:Ketones; D012997:Solvents