Enol phosphates, cross coupling

Cahiez and Avedissian further reported the cross-coupling reaction of cheap and easily available enol phosphates [10]. These substrates are less reactive, which explains the higher catalyst loadings and 2 equiv. of Grignard reagent are required (Scheme 5.5). 

Scheme 5.5 Iron-catalyzed cross-coupling reaction of an enol phosphate reported by Cahiez and Avedissian.

A new cyclising reagent is proposed for the synthesis of 5-unsubstituted 1,3,4-thiadiazoles (133). The latter are formed in good yield by the reaction of thiohydrazides (134) with diethyl chlorophosphate (Scheme 39). A useful, one-pot protocol has been developed for the conversion of enolizable ketones (135) to alkylated or arylated olefins (136) by Pd-catalysed cross coupling of in-situ generated enol phosphates (137) with Grignard reagents (Scheme 40). ... 

Enol phosphates derived from iV-acyl-piperidin-2-one (or 2-oxoazepane) can be utilized in cross-coupling... 

Hydroboration of exocyclic enol ether 111 with 9-BBN and following Suzuki-Miyaura reaction with enol triflate 128 proceeded smoothly to generate the cross-coupled product 129 in 81% yield (Scheme 17). Not unexpectedly, the corresponding enol phosphate of 128 proved to be a poor substrate for this complex fragment coupling. Given the structural complexity and sheer size of the respective fragments, this remarkable yield (81%) represents... 

C-C bond formation via transition-metal-catalysed cross coupling of -activated enols has been reviewed (97 references) while less reactive than systems involving halide or triflate leaving groups, vinyl phosphates have significant advantages in terms of cost, stability, and low toxicity... 

Scheme 5.51 Fe-catalyzed cross-coupling of alkylmagnesium reagents with enol phosphates and enol pivalates under ligand-free conditions [143, 144].

Specific phosphate reagents have involved enol phosphates and ketene acetal phosphates that have been utilized in the Suzuki-Miyaura and Stille cross-coupling carbon-carbon bond formation reactions as well as tetra-benzylpyrophosphate, used for the first time as a dehydrating agent for synthesis of carboxamides. 

The Pd-catalysed P-C cross-coupling reaction between a-amido enol phosphates (67) and secondaiy phosphine-borane complexes (70) or phosphine oxides (71) afforded under mild condition hindered tertiary a-enamido phosphine derivatives (68) or (69) with up to 99.4% ee and in up to 70% chemical yields (Scheme 22). ... 

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