Trialkylsilyl triflate mediated functionalization of carbonyl compounds

Abstract

Trialkylsilyl triflates promoted addition reactions of dimethyl sulfide, pyridine, triphenylarsine and triphenylphosphine to carbonyl compounds such as aldehydes, $\alpha,\beta$-acetylenic acetals, $\alpha,\beta$-enals, $\alpha,\beta$-enones have been studied. Several important findings have been found by the low temperatuer $^1H$-NMR spectroscopy. First, the addition reactions occurred at low temperature in dichloromethane and tetrahydrofuran. Second, arsoniosilylation of $\alpha,\beta$-enones and enals occurred cleaniy via 1,4-addition mode, whereas pyridiniosilylation of $\alpha,\beta$-enals and triphenylphosphorylation of $\alpha,\beta$-acetylenic acetals proceeded via the 1,2-addition mode at low temperature. Third, allylic 1,3-rearrangement of 1-alkoxyallylpyridinium salts to 3-alkoxyallylpyridinium salts were observed but no 1,3-rearrangement of 1-alkoxy-2-alkynylphosphonium salts was observed. Fourth, dimethyl sulfide and triphenylphosphine could form the corresponding salts not with ketones but with aldehydes in the presence of trimethylsilyl triflate (TMSOTf). Finally, the reaction of $\alpha,\beta$-enones vis arsoniosilylation was reversible reaction. $\alpha$-Alkoxyalkylation of $\alpha,\beta$-enones could be carried out by the reaction of $\beta$-pyridinium salt silyl enol ethers with saturated and unsaturated acetals, followed by elimination of pyridine by using 1,8-diazabicyclo[5,4,0] undec-7-ene(DBU). Also, $\beta$-arsonium salt silyl enol ethers derived from $\alpha,\beta$-enals, triisopropylsilyl triflate and triphenylarsine are important intermediates for the reactive ylide. Furans were prepared in good yields by the reaction of the arsonium ylides and aldehydes. On the other hand, acetylenic acetals with triphenylphosphine and trimethylsilyl triflate (TMSOTf) afforded thermally stable 1-alkoxy-2-alkynylphosphonium salts. Generation of ylides was followed by treatment with the aldehydes in the presence of chlorotrimethyl silane(TMSCI) to affo...