Chemoselectivity phosphates

Allylic phosphates are more reactive than allylic acetates. Chemoselective reaction of the allylic phosphate moiety of the bis-allylic compound 88 with one equivalent of malonate, without attacking the allylic acetate moiety, takes place to give 89. Then the aminated product 90 was obtained by the addition of amine [52],... 

CPL spectroscopy may also be used to signal the nature of the ternary anion adduct. In the series of phospho-anion complexes of [Eu.la]3+, Figure 5, complexes of HP042 and glucose-6-phosphate give identical CPL spectra - consistent with their very similar NMR spectral profile. Adducts with phospho-tyrosine, N-acetyl phospho-Tyr and a short peptide (phosphorylated at the Pyr residue) are also near-identical, consistent with chemoselective binding of the Tyr-OP phospho-anion. 

Woerpel and Clark identified silver phosphate as the optimal catalyst to promote di-ferf-butylsilylene transfer from cyclohexene silacyclopropane to a variety of substituted alkynes (Scheme 7.25).95 While this silver salt exhibited attenuated reactivity as compared to silver triflate or silver trifluoroacetate, it exhibited greater functional group tolerance. Both di- and monosubstituted silacyclopropenes were easily accessed. Terminal alkynes are traditionally difficult substrates for silylene transfer and typically insert a second molecule of the starting acetylene.61,90 93 Consequently, the discovery of silver-mediated silylene transfer represents a significant advance as it enables further manipulation of monosubstituted silacyclopropenes. For enyne substrates, silylene transfer the alkynyl group was solely observed. The chemoselectivity of the formation of 99f was attributed to ring strain as theoretical calculations suggest that silacyclopropenes are less strained than silacyclopropanes.96 97... 

A practical synthesis of 1,3-OX AZEPINES VIA PHOTOISOMERIZATION OF HETERO AROMATIC V-OXIDES is illustrated for 3,1-BENZOXAZEPINE. A hydroboration procedure for the synthesis of PERHYDRO-9b-BORAPHENALENE AND PERHYDRO-9b-PHEN-ALENOL illustrates beautifully the power of this methodology in the construction of polycyclic substances. The conversion of LIMONENE TO p-MENTH-8-EN-YL METHYL ETHER demonstrates a regio-and chemoselective method for the PHOTOPROTONATION OF CYCLOALKENES. An efficient method for the conversion of a ketone to an olefin involves REDUCTIVE CLEAVAGE OF VINYL PHOSPHATES. A mild method for the conversion of a ketone into the corresponding trimethylsiloxy enol ether using trimethylsilyl acetate is shownforthe synthesis of (Z)-3-TRIMETHYLSILOXY-2-PENTENE. 

Allylic halides are not as readily accessible as allylic alcohols or their ester derivatives. Thus, the requirement that allylic halides must be used as precursors for carbonyl addition reactions in conjunction with magnesium and other similar reductants is a severe restriction limiting the convenience of these routes to homoallylic alcohols. In this regard, samarium diiodide can be used to great advantage, because substrates other than allylic halides are suitable precursors for such transformations. For example, allylic phosphate esters have been reported to couple with carbonyl substrates in the presence of Smh (equation 15). Since esters and nitriles are unreactive under these conditions, the Smh-mediated process is likely to be more chemoselective than those promoted by magnesium or lithium. 

Yoneda, R., Harusawa, S., and Kurihara, T., Cyano phosphate, an efficient intermediate for the chemoselective conversion of carbonyl compounds to nitriles, J. Org. Chem., 56, 1827, 1991. 

The hT-benzenesulfonylprolinate catalyst, (3) of Fig. 1, provided the highest levels of stereocontrol. The binaphthyl hydrogen phosphate rhodium (II) catalyst also promoted chromanone formation and while the cis-diastereoselectivity was excellent (94%), the enantiocontrol was modest (33% ee) application of this catalyst to the P-lactam-forming C-H insertion reaction in Eq. (39) revealed high chemoselectivity (93% yield of trans),hut low enantioselectivity (26% ee) [28]. 

Scheme 3, Chemoselective glycosylation using gfycosyl phosphates.

The relative reactivity of the derivatives follows the trend allyl carbonate > allyl phosphate > allyl acetate (see Equations 20.5-20.7)." This difference in reactivity allows for chemoselective substitutions of one allylic alcohol derivative over another. Other allylic electrophiles, such as allylic sulfonates, which undergo cleavage of the carbon-sulfur bond, allylic nitro compounds, which undergo cleavage of the C-N bond, - and allylic... 

Chemoselective Hydrolysis of Phosphate Esters. Chemical hydrolysis of polyprenyl pyrophosphates is hampered by side reactions due to the lability of the molecule. Hydrolysis catalyzed by acid phosphatase - an enzyme named because it displays its pH-optimum in the acidic range - readily afforded the corresponding dephosphorylated products in acceptable yields [511]. 

Scheme 2.76 Chemoselective enzymatic hydrolysis of phosphate esters...

Pore et al. (2006) documented the thia-Michael addition involving the conjugate addition of thiols to a,p-unsaturated ketones in the presence of SSA as a heterogeneous catalyst under solvent-free conditions at room temperature (Scheme 5.53). The catalytic activity was comparatively studied with potassium phosphate. Studies revealed that SSA is suitable for electron-deficient a,P-unsaturated compounds, whereas K3PO4 catalyzed the reactions of both electron-deficient as well as electron-rich enones. SSA catalyzes a rapid, green, and chemoselective aza-Michael addition of amines and thiols... 

Their reactivities are different. Although allylation with allylic chlorides proceeds without a Pd catalyst, their reaction is accelerated in the presence of a Pd catalyst. Allylic alcohols are rather poor substrates. Instead, their esters, typically allylic acetates, are used for smooth allylation. Allylic phosphates are more reactive than allylic acetates, and the chemoselective reaction of the allylic phosphate moiety of the bis-allylic compound with 1 equiv of malonate without attacking the allylic acetate moiety occurs (Scheme 5). Then the aminated product is obtained by the addition of amine. In addition to allylic esters, even allylic nitro compounds i-Piand sulfonest Hio] aHyiatjoj, Reactions of... 

Miscellaneous. Allylic phosphates have found applications in T7-allyl palladium chemistry. It has been demonstrated that allylic phosphates undergo oxidative addition more readily than the corresponding acetate, such that chemoselectivity could be achieved when these functionalities were present in the same molecule (eq 17).2 Finally, p-keto phosphonates were coupled with epoxides to provide useful yields of spirocyclopropanes (eql8).2 ... 

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