On the Paterno-Buchi reaction of chiral phenylglyoxylate esters with furan derivatives

摘要

The reaction of (S')-l-methylpropylbenzoylformate with furan gave (1'S)-1'-methylpropyl (1S,5R,6R)-6alpha-phenyl-2,7-dioxabicyclo3.2.0hept-3-en-6beta-carboxylate with de=15.The reaction of (S)-2-methylbutyl benzoylformate with furan gave (2'S)-2-methylbutyl (1SR,,5RS,6RS)-6alpha-phenyl-2,7-dioxabicyclo3.2.0hept-3-en-6beta-carboxylate as a mixture of stereoisomers.(lR,2S,5R)-5-Methyl-2-(l-methylphenylethyl)cyclohexyl benzoylformate gave (1R,2S,5R)-5-methyl-2-(1-methylphenylethyl)cyclohexyl (1R,5S,6S)-6alpha-phenyl-2,7-dioxabicyclo3.2.0hept-3-en-6beta-carboxylate with de=95.The stereochemical behaviour can be explained considering the energy gap between the biradical intermediates in the coupling reaction.When the reaction was performed in the presence of zeolite,the diastereo-isomeric excess increased (37,18 and 98,respectively).The reaction of (S)-1-methylpropylbenzoylformate with 2-methylfuran gave (1'S)-1'-methylpropyl (1S,5R,6R)-l-methyl-6alpha-phenyl-2,7-dioxabicyclo3.2.0hept-3-en-6beta-carboxylate (yield:12) with de=94.The main product was (1'S)-1'-methylpropyl (lSR,5RS,6RS)-3-methyl-6alpha-phenyl-2,7-dioxabicyclo3.2.0hept-3-en-6beta-carboxylate as a mixture of diastereoisomers.The reaction of (S)-2-methylbutyl benzoylformate with 2-methylfuran gave (2'5')-2-methylbutyl (1S,5R,6R)-l-methyl-6a-phenyl-2,7-dioxabicyclo3.2.0hept-3-en-6beta-carboxylate (yield:9) with de=10.The main product was (2'5)-2-methylbutyl (1SR,5RS,6RS)-3-methyl-6alpha-phenyl-2,7-dioxabicyclo3.2.0hept-3-en-6beta-carboxylate as a mixture of stereoisomers.The stereochemical behaviour can be explained on the basis of the energy gap between the possible biradical intermediates.The reaction of (S)-l-methylpropylbenzoylformate and (S)-2-methylbutyl benzoylformate with 2-furylmethanol gave the corresponding adducts as a mixture of diastereoisomers.The reaction of (S)-l-methyl-propylbenzoylformate and (S)-2-methylbutyl benzoylformate with 2-furylphenylmethanol gave the corresponding adducts with high diastereoselectivity.In this case,the stereochemical behaviour is determined by the presence of the hydroxy group in a molecule with a preferntial conformation.