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[摘要]：Allenyl phosphine oxides R2R3C:C:CR1P(O)Ph2 (1a-l) undergo stereoselective iodohydroxylation by reaction with I2/H2O in MeCN, giving 3-phosphinylallyl alcs. (E)-HOCR2R3CI:CR1P(O)Ph2 (2a-l; R1, R2, R3 = H, Me, Et, n-Pr, C5H11, Ph). The compds. 1 were easily prepd. by reaction of the corresponding propargyl alcs. R1CYCC(OH)R2R3 with Ph2PCl. Optically active allenyl phosphine oxides RCH:C:CHP(O)Ph2 [(R)-, (S)-1c, R = Me; (R)-, (S)-1e, R = C5H11] gave the corresponding chiral allyl alcs. HOCHRCI:CHP(O)Ph2 [(R)-(E)- and (S)-(E)-2c and -2e, resp.] with >98% ee. Two sets of reaction conditions were established to enable the highly regio- and stereoselective iodohydroxylation of the compds. 1. The scope of this reaction was examd. extensively. Notably, studies on the reactivity of optically active substrates indicated that the axial chirality in the starting allenes may be efficiently transferred to the center chirality of the products with no discernible loss of enantiopurity. Due to the importance of phosphine-contg. compds., both as reagents and ligands, this reaction shows potentials in org. synthesis. Investigations using ESI-MS technol. on the 18O-labeled product, which was prepd. using 18O-water as the solvent, indicated that the 18O atom was bound to phosphorus in the final product and the oxygen atom of the hydroxyl comes from the phosphinyl functionality of the allene reactant. These results provided solid evidence for the formation of a five-membered cyclic intermediate from the neighboring group participation of the diphenylphosphinyl group. To the best of our knowledge, this is the first time that the neighboring group participation of this type of group was obsd. |
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