Preparation method of propyl malonic acid and homologues thereof

The invention relates to a preparation method of a compound as shown in a chemical structural formula I. The preparation method comprises the following steps: selecting malonic acid diester and 1-chloroalkane, and carrying out monoalkylation under the action of alkali to prepare monoalkyl malonic acid as shown in the formula I; the preparation reaction is as follows: R1 and R2 are respectively selected from benzyl, C1-C5 straight-chain alkyl or C3-C5 branched-chain alkyl; y is selected from C1-C4 straight chain alkyl or C3-C4 branched chain alkyl; the PTC (Positive Temperature Coefficient) of the catalyst is selected from R4NX or R3R1NX; wherein R is selected from straight-chain alkyl with 1 to 4 carbon atoms and straight-chain alkyl with 5 to 8 carbon atoms; r1 is PhCH2, a straight chain alkyl group with 1 to 5 carbon atoms or a straight chain alkyl group with 6 to 18 carbon atoms; wherein X is Cl, Br or I. 本发明涉及化学结构式Ⅰ所示的化合物的制备方法：选择丙二酸二酯与1-氯代烷，在碱作用下，单烷基化制得Ⅰ所示的单烷基丙二酸；其制备反应如下：R1和R2分别选自：苄基、C1～C5直链烷基或C3～C5支链烷基；Y