A novel 7-hydroxyprostaglandin E.sub.1, or a stereoisomer thereof, or a protected derivative thereof, having the following formula: ##STR1## wherein R.sup.8 represents H, CH.sub.3 or C.sub.2 H.sub.5, R.sup.9 represents H or CH.sub.3, R.sup.10 and R.sup.11 are identical or different, and each represents H, tetrahydropyranyl or t-butyldimethylsilyl. Also provided is a process for producing an adjacently disubstituted ketone including the above compounds, i.e. 7-oxoprostaglandin, etc. which comprises reacting an .alpha.,.beta.-unsaturated carbonyl compound with a cuprous salt and an organolithium compound in an aprotic inert organic medium in the presence of trialkylphosphine, the amounts of said cuprous salt and said organolithium compound being substantially equimolar, and reacting the product with a protected acetal derivative of an organic carbonyl compound or an aldehyde in the presence of a Lewis acid, if necessary, followed by reacting the product with a proton donor.