Reactivity and Selectivity of Ortho-Metalated Rhodium(II) Complexes in C−H Insertion Reactions of α-Diazo Compounds

Abstract

Regioselective intramolecular C−H insertion reactions of α-diazo β-keto esters and α-diazo ketones are mediated by Rh2[OOCR]4 - x [PC] x (x = 1, 2; PC = ortho-metalated phosphine; R = CH3, C3F7). In particular, the intramolecular transformation of 1-diazo-5-methyl-3-propyl-2-hexanone catalyzed by Rh2[OOCCH3]2[PC]2 (PC = (C6H4)P(C6H5)2, head-to-tail (H−T) configuration) afforded only the tertiary C−H insertion product. By comparison, no C−H insertion reaction was promoted by doubly metalated complexes with a head-to-head (H−H) configuration. Rh2[OOCR]3[PC] compounds were found to be less suited for these type of reactions.

Enantiocontrol in the intermolecular cyclopropanation reaction catalyzed by dirhodium(ii) complexes with ortho-metalated aryl phosphine ligands

“…13,14 Those with high electronwithdrawing carboxylate groups (CF 3 CO 2 ) have shown the best selectivity values.…”

Functionalization of Carbon–Hydrogen Bonds Through Transition Metal Carbenoid Insertion

“…3 [25][26][27][28][29][30], but to date they tend to give low enantioselectivities and will not be discussed in this chapter. In addition, chiral auxiliaries are sometimes utilized instead of or in addition to chiral catalysts to control stereoselectivity [31][32][33][34], but this is becoming increasingly less popular as the catalysts become more selective.…”

“…4) over their five-membered ring counterparts [70]. They examined a number of chiral dirhodium catalysts, and Rh 2 (S-DOSP) 4 (26) in refluxing pentane generally provided the best enantioinduction, with enantioselectivities ranging from 41 to 69% ee.…”

“…This opens up the opportunity for asymmetric catalysis to occur. Indeed, when a number of aryldiazoacetates 74 were decomposed with Rh 2 (S-DOSP) 4 (26) in the presence of cyclohexane, up to 95% ee was achieved for 77 [79,81]. A fluorous prolinate catalyst was also developed to facilitate purification, but the enantioselectivities were not as high [82].…”

“…A number of catalysts have been used for this transformation, with varying results (Scheme 25). Davies and coworkers have used Rh 2 (S-DOSP) 4 (26) as the catalyst, obtaining 114 in yields ranging from 48 to 74%, diastereoselectivities from 1.6:1 to 4.0:1, and up to 98% ee [79,81]. It was noted that the highest enantioselectivity was obtained not in neat THF, but when the reactions were conducted in hexanes at −50 °C with two equivalents of THF.…”