2-Hydroxyphenoxyacetic acid

Faulkner and Woodstock (1964) reported the soil microorganism Aspergillus niger degraded 2,4-D to 2,4-dichloro-5-hydroxyphenoxyacetic acid. 

The stannane was introduced using the directed ort/io-metalation reaction followed by addition of trimethyltin chloride to give 168. Hydroboration of arylstannane 168 with 9-BBN and oxidative work-up with basic peroxide provided the primary alcohol 169. Mitsunobu reaction of this alcohol with the cyanomethyl ester of 4-hydroxyphenoxyacetic acid afforded preactivated ester derivative 170 in good yield (Scheme 4.2.1). 

Figure 19 2,4-D, analogues and nonrelated probes studied in MIAs [18,23,51,52,53,55,63]. 2,4-D, 2,4-dichlorophenoxyacetic acid CPOAC, 4-chlorophenoxyacetic acid POAC, phenoxy-acetic acid CMMC, 7-carboxy-methoxy-4-methylcoumarin HGA, homogentisic acid (2,5-dihydroxyphenylacetic acid) 2-C-4-H, 2-chloro-4-hydroxyphenoxyacetic acid.

Dichloro-4-hydroxyphenoxyacetic acid was the predominant product identified in several weed species as well as smaller quantities of 2-chloro-4-hydioxyphenoxyacetic acid in wild buckwheat, yellow foxtail and wild oats (Fleeker and Steen, 1971). 

Coupling of 69 with methyl 4-hydroxyphenoxyacetate 70 was carried out in the presence of imidazole and confirmed by gel-phase 13C NMR of PSDES resin 71. The hydrolysis of resin-bound ester was efficiently achieved using trimethyltin hydroxide (TMTOH) [110-114] to give the corresponding immobilized carboxylic acid 72. For the key Staudinger reaction, activation of the carboxylic acid 72 by Mukaiyama s reagent 74 was employed (Scheme 20) [115-117]. The m-p-lactam 16 was obtained in a 12-14% isolated yield. 

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