The stereochemistry of 1-alkylallylpotassium compounds

Allyl Calcium Compounds: Synthesis and Structure of Bis(η3-1-alkenyl)calcium

“…Given the unsymmetrical substitution pattern of the ligand, endo / exo isomerism of the trihapto 1-methylallyl anion could be observed in the NMR spectra recorded in THF- d 8 at room temperature (Scheme ). As reported earlier, the potassium derivative 1-K exists almost exclusively as the endo stereoisomer according to its 1 H and 13 C NMR spectrum (see below for discussion) . In contrast, two sets of broad proton signals can be observed for the η 3 -bonded allyl ligand in 2-Ca .…”

“…Since unambiguous assignment of endo and exo proton signals can be made only from their coupling constants, the ratio of endo/exo = 60:40 was determined from integration of the corresponding 13 C NMR signals, which can be distinguished by their chemical shifts. 23,24 1 H and 13 C NMR spectroscopic analysis shows that 1-K and 1-Ca give rise to similar spectra, consistent with a symmetrical η 3coordination mode of the butenyl ligands. The 1 H NMR resonances observed at 6.14 (H β ), 2.49 (H γ ), 1.86 (H Rcis ), and 1.60 ppm (H Rtrans ) for 1-K and at 5.95-6.19 (H β ), 3.15-3.35 (H γ ), and 1.53 ppm (H R ) for 1-Ca undergo a strong downfield shift for the γ-position of the allyl fragment when going from the potassium to the calcium derivative.…”

“…As reported earlier, the potassium derivative 1-K exists almost exclusively as the endo stereoisomer according to its 1 H and 13 C NMR spectrum (see below for discussion). 23 In contrast, two sets of broad proton signals can be observed for the η 3 -bonded allyl ligand in 2-Ca. Since unambiguous assignment of endo and exo proton signals can be made only from their coupling constants, the ratio of endo/exo = 60:40 was determined from integration of the corresponding 13 C NMR signals, which can be distinguished by their chemical shifts.…”

“…In contrast, two sets of broad proton signals can be observed for the η 3 -bonded allyl ligand in 2-Ca . Since unambiguous assignment of endo and exo proton signals can be made only from their coupling constants, the ratio of endo / exo = 60:40 was determined from integration of the corresponding 13 C NMR signals, which can be distinguished by their chemical shifts. , …”

“… a Data taken from ref ; endo / exo compositions determined by 13 C NMR spectroscopy or by correlation with the cis / trans ratios after derivatization with electrophiles. b Data reported in ref were reproduced in this work. c Data taken from ref ; endo / exo compositions determined by correlation with the cis / trans ratios after derivatization with electrophiles. Note that magnesium bears a rotating σ instead of a η 3 allyl ligand. …”