Method for producing phosphorus-containing alpha-keto acid

A method for producing a compound represented by the following formula (7),

• said method comprising:
• (a) a compound represented by the following formula (1) is reacted with a compound represented by the following formula (2) under the existence of an acid or the existence of a condensation agent and a base
• [wherein, R1 represents C1-4 alkyl group, arylmethyl group, or substituted arylmethyl group];
• or
• the compound of formula (1) is reacted with a compound represented by the following formula (3) under the existence of a base
• R1X (3)
• [wherein, R1 represents the same meaning as aforementioned, and X represents halogen atom];
• or
• the compound of the formula (1) is reacted with isobutylene under the existence of an acid catalyst;
• to produce a compound represented by the following formula (4);
• [wherein, R1 represents the same meaning as aforementioned],
• thereafter,
• (b) the compound of formula (4) is reacted with a compound represented by the following formula (5) under the existence of a base of 2-3 equivalents based on the compound of formula (4);
• (COOR2)2 (5)
• [wherein, R2 represents C1-4 alkyl group, arylmethyl group, or substituted arylmethyl group]
• to produce a compound represented by the following formula (6);
• [wherein, R1 and R2 represent the same meaning as aforementioned];
• and further,
• (c) the compound of formula (6) is hydrolyzed under the existence of an acid to be subjected to decarboxylation.