On the deprotonation of η6-1,3-dimethoxybenzene-Cr(CO)3 derivatives: Influence of the reaction conditions on the regioselectivity

ortho‐Directing Chromium Arene Complexes as Efficient Mediators for Enantiospecific C(sp2)–C(sp3) Cross‐Coupling Reactions

“…Importantly,w hen enantioenriched 2a (er = 96:4) was used, 3aa was obtained with identical enantiomeric excess,t hus indicating that the reaction occurs with perfect enantiospecificity (Table 1). [11] To highlight the synthetic utility of this method for latestage modification, the estradiol-derived chromium complex 1k was selectively coupled in the 6-position with the boronic esters 2a and ent-2a to give the diastereomeric products 3ak and 3ak' ',r espectively,i nh igh yields and with complete diastereoselectivity (Table 1). Perfect ortho-selectivity was also observed for the products 3ac and 3ad,c ontaining ethoxy and isopropoxy directing groups,r espectively.Aseries of functional groups [i.e., alkyl (3ad), CF 3 (3ae), Cl (3af), OTIPS (3g), OMe (3h), and NMe 2 (3j)] were well tolerated and the C(sp 2 )-C(sp 3 )c ross-coupling occurred selectively ortho to the methoxy substituent.…”

Transition Metal Arene π-Complexes in Organic Synthesis and Catalysis

“…When two methoxy groups are meta to each other, lithiation first occurs between them at the 2-position [114][115][116]. When the 2-position of the m-dimethoxybenzene complex is blocked (as in 24), lithiation occurs at the 5-position (in 25) when lithium amide base is used, and at the 4-position (in 26) when n-BuLi is used [25,31,114].…”

“…When the 2-position of the m-dimethoxybenzene complex is blocked (as in 24), lithiation occurs at the 5-position (in 25) when lithium amide base is used, and at the 4-position (in 26) when n-BuLi is used [25,31,114]. The 5-lithio-species was shown to be a kinetic product that isomerizes to a 4-lithio-intermediate at 0 °C [114] (Scheme 1).…”

“…Entries 2-4 show that variation of reaction temperatures from -100 °C to 0 °C has no significant effect in that highly selective system. Cyano-stabilized nucleophiles, on the other hand, give mixtures of mand p-addition products [114]. Table 4 also includes results with para directing substituents, CF 3 and Me 3 Si (entries 14 and 15).…”

“…The complex TpMo(NO)(MeIm)(naphthalene) (114) has been prepared from the hexacarbonyl according to the sequence outlined in Fig. 24.…”