##STR00001##

The present invention relates to a method for preparing 4-hydroxy-2-methylene-butanal, 4-hydroxy-2-methyl-but-2-enal and esters thereof of the formula (I.a) and (I.b) where R.sup.1 is as defined in the claims and the description, by subjecting isoprenol or an ester thereof to a photooxidation in the presence of a photosensitizer and an acylating agent. The invention relates moreover to certain hydroperoxides of the compounds (I.a) or (I.b), and to the use thereof as intermediates in the synthesis of compounds (I.a) and (I.b) or in the synthesis of retinol, stereoisomers and derivatives thereof.

The present invention provides 5-(2-butyl-1,3-dioxolan-2-yl)-1-methylpentyl acetate of the following formula (1).

The present invention further provides the aforesaid 5-(2-butyl-1,3-dioxolan-2-yl)-1-methylpentyl acetate (1), the process comprising the step of subjecting an organic magnesium compound (2) of the following general formula (2), wherein X.sup.1 represents a halogen atom or a 3-(2-butyl-1,3-dioxolan-2-yl) propyl group, to a nucleophilic addition reaction with propylene oxide of the following formula (3) and then reacting with an acetylating agent of the following general formula (4), wherein X.sup.2 represents a halogen atom, an acetoxy group, a methoxy group, or an ethoxy group, to form 5-(2-butyl-1,3-dioxolan-2-yl)-1-methylpentyl acetate (1).

##STR00001##

The present invention provides 5-(2-butyl-1,3-dioxolan-2-yl)-1-methylpentyl acetate of the following formula (1).

The present invention further provides the aforesaid 5-(2-butyl-1,3-dioxolan-2-yl)-1-methylpentyl acetate (1), the process comprising the step of subjecting an organic magnesium compound (2) of the following general formula (2), wherein X.sup.1 represents a halogen atom or a 3-(2-butyl-1,3-dioxolan-2-yl) propyl group, to a nucleophilic addition reaction with propylene oxide of the following formula (3) and then reacting with an acetylating agent of the following general formula (4), wherein X.sup.2 represents a halogen atom, an acetoxy group, a methoxy group, or an ethoxy group, to form 5-(2-butyl-1,3-dioxolan-2-yl)-1-methylpentyl acetate (1).

##STR00001##

The present invention relates to a novel method for producing an intermediate expressed by chemical formula 5 that can be effectively used in synthesis of sphingosine-1-phosphate receptor agonist.

The present invention relates to a novel method for producing an intermediate expressed by chemical formula 5 that can be effectively used in synthesis of sphingosine-1-phosphate receptor agonist.