Branching out with hydrogen: Hydrogenation of symmetric or mixed carboxylic anhydrides in the presence of styrenes or activated olefins generates intermolecular hydroacylation products. The use of cationic rhodium catalysts ligated by triphenylarsine (Ph3As) results in the formation of branched coupling products as single regioisomers in high yields (see scheme; cod=cycloocta‐1,5‐diene, ArF=3,5‐(CF3)2C6H3).
An efficient route to α‐methylene‐γ‐lactones involves the Ru‐catalyzed [2+2+1] cycloadditions of allenyl aldehydes and ketones with CO (see scheme; n = 1, 2; R = H, CH3; X = NTs, O, C(CO2Et)2; Ts = toluene‐4‐sulfonyl). The α‐methylene‐γ‐lactone moiety is found in numerous biologically active natural products.
Treatment of alkynylsilanes with triarylantimony diacetates in the presence of Pd 2 (dba) 3 ؒCHCl 3 (5 mol%) and CuI (10 mol%) in CH 3 CN at 50 ЊC for 5 h afforded aryl-substituted alkynes in good yield. Alternatively, direct carbonylative coupling of triarylantimony diacetates with alkynylsilanes was accomplished under atmospheric pressure of carbon monoxide. This coupling was extended to carbonylative cross-coupling of silanes with antimony() compounds. The results are summarized in Scheme 4 and Table 2.
Catalytic hydrogenation of 1,3-enynes 1a-8a in the presence of ethyl glyoxalate at ambient pressure and temperature using a rhodium catalyst modified by (R)-(3,5-tBu-4-MeOPh)-MeO-BIPHEP results in highly regio- and enantioselective reductive coupling to furnish the corresponding alpha-hydroxy esters 1b-8b. As demonstrated by the elaboration of alpha-hydroxy ester 1b, the terminal and internal olefin moieties embodied by the diene side chain are subject to selective manipulation, one over the other.
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