TY  - JOUR
A1  - Lood, Kajsa
A1  - Tikk, Triin
A1  - Krüger, Mandy
A1  - Schmidt, Bernd
T1  - Methylene capping facilitates cross-metathesis reactions of enals
BT  - a short synthesis of 7-methoxywutaifuranal from the xylochemical isoeugenol
JF  - The journal of organic chemistry
N2  - Four combinations of type-I olefins isoeugenol and 4-hydroxy-3-methoxystyrene with type-II olefins acrolein and crotonaldehyde were investigated in cross-metathesis (CM) reactions. While both type-I olefins are suitable CM partners for this transformation, we observed synthetically useful conversions only with type-II olefin crotonaldehyde. For economic reasons, isoeugenol, a cheap xylochemical available from renewable lignocellulose or from clove oil, is the preferred type-I CM partner. Nearly quantitative conversions to coniferyl aldehyde by the CM reaction of isoeugenol and crotonaldehyde can be obtained at ambient temperature without a solvent or at high substrate concentrations of 2 mol.L-1 with the second-generation Hoveyda-Grubbs catalyst. Under these conditions, the ratio of reactants can be reduced to 1:1.5 and catalyst loadings as low as 0.25 mol % are possible. The high reactivity of the isoeugenol/crotonaldehyde combination in olefin metathesis reactions was demonstrated by a short synthesis of the natural product 7-methoxywutaifuranal, which was obtained from isoeugenol in a 44% yield over five steps. We suggest that the superior performance of crotonaldehyde in the CM reactions investigated can be rationalized by "methylene capping", i.e., the steric stabilization of the propagating Ru-alkylidene species.
KW  - Aldehydes
KW  - Catalysts
KW  - Hydrocarbons
KW  - Metathesis
KW  - Mixtures
Y1  - 2022
U6  - https://doi.org/10.1021/acs.joc.1c02851
SN  - 0022-3263
SN  - 1520-6904
VL  - 87
IS  - 5
SP  - 3079
EP  - 3088
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Riemer, Nastja
A1  - Riemer, Martin
A1  - Krüger, Mandy
A1  - Clarkson, Guy J.
A1  - Shipman, Michael
A1  - Schmidt, Bernd
T1  - Synthesis of arylidene-beta-lactams via exo-selective Matsuda-Heck arylation of methylene-beta-lactams
JF  - The journal of organic chemistry : JOC
N2  - exo-Methylene-beta-lactams were synthesized in two steps from commercially available 3-bromo-2-(bromomethyl)-propionic acid and reacted with arene diazonium salts in a Heck-type arylation in the presence of catalytic amounts of Pd(OAc)(2) under ligand-free conditions. The products, arylidene-beta-lactams, were obtained in high yields as single isomers. The beta-hydride elimination step of the Pd-catalyzed coupling reaction proceeds with high exo-regioselectivity and E-stereoselectivity. With aryl iodides, triflates, or bromides, the coupling products were isolated only in low yields, due to extensive decomposition of the starting material at elevated temperatures. This underlines that arene diazonium salts can be superior arylating reagents in Heck-type reactions and yield coupling products in synthetically useful yields and selectivities when conventional conditions fail.
Y1  - 2021
U6  - https://doi.org/10.1021/acs.joc.1c00638
SN  - 0022-3263
SN  - 1520-6904
VL  - 86
IS  - 13
SP  - 8786
EP  - 8796
PB  - American Chemical Society
CY  - Washington
ER  -