Abstract
We conducted diastereodifferentiating [2+2] photocycloadditions of cyclo-hexenones modified with a chiral 8-(p-methoxy phenyl)menthyl auxiliary with olefins in water. Although the photoreaction didn’t proceed at all in pure water owing to very low solubility, the use of surfactants [sodium dodecyl sulfate (SDS) or dodecylamine hydrochloride (DAH)] and additive (organic solvent) enabled the reactions to progress with moderate to high conversions and yields. Furthermore, we synthesized a new menthol derivative substrate containing a (p-octyloxy)phenyl group for enhancing hydrophobicity, and elucidated that this new substrate was found to be a suitable chiral auxiliary in this asymmetric photoreaction in aqueous system. The additive effect of organic molecules on the yield and diastereoselectivity of the photo-adducts is also discussed.
Highlights
Within organic synthetic chemistry, environmentally friendly reaction systems have attracted a great deal of attention as “green chemistry” [1,2,3,4]
Surfactants orient themselves in aqueous media to generate micelles, which due to the hydrophobic interaction include organic molecules inside
For the assembly of a new-type chiral auxiliary, 1b was prepared from (R)-(+)-pulegone according to our previous procedure modifying Corey’s method [12,13,14,19,20,21]
Summary
Within organic synthetic chemistry, environmentally friendly reaction systems have attracted a great deal of attention as “green chemistry” [1,2,3,4] In these reactions, water is the most versatile reaction medium owing to its unique nature, nontoxicity, abundance, low cost and ease of waste treatment. In contrast with conventional thermal reactions, it is well known that photochemical [2+2] cycloaddition readily gives the distorted cyclobutane skeleton Because this skeleton is synthetically versatile, for natural-product precursors such as terpenoids with polyquinane skeletons and various unique compounds, much effort has been dedicated to this reaction, especially asymmetric [2+2] photoreaction [9,10]. We discuss the suitable menthol auxiliary and additive effect of organic molecules on yield and selectivity in both aqueous and organic reaction systems
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