2,464 research outputs found
Dienes, Louis -- 1939-42 -- Correspondence, Individual -- letter, 1941-10-17
No full textLetter from Dienes, Louis to Sabin, Albert B. dated 1941-10-17.Sabin Collection Fair Use Policy</a
Dienes, Louis -- 1939-42 -- Correspondence, Individual -- letter, 1939-06-02
No full textLetter from Dienes, Louis to Sabin, Albert B. dated 1939-06-02.Sabin Collection Fair Use Policy</a
Dienes, Louis -- 1939-42 -- Correspondence, Individual -- letter, 1942-05-25
No full textLetter from Sabin, Albert B. to Dienes, Louis dated 1942-05-25.Sabin Collection Fair Use Policy</a
Dienes, Louis -- 1939-42 -- Correspondence, Individual -- letter, 1941-10-01
No full textLetter from Sabin, Albert B. to Dienes, Louis dated 1941-10-01.Sabin Collection Fair Use Policy</a
Dienes, Louis -- 1939-42 -- Correspondence, Individual -- letter, 1941-10-20
No full textLetter from Sabin, Albert B. to Dienes, Louis dated 1941-10-20.Sabin Collection Fair Use Policy</a
Dienes, Louis -- 1939-42 -- Correspondence, Individual -- letter, 1940-11-15
No full textLetter from Sabin, Albert B. to Dienes, Louis dated 1940-11-15.Sabin Collection Fair Use Policy</a
Pleuropneumonia -- 1946-49 -- Other Diseases Researched, Miscellaneous -- letter, 1948-05-27
No full textLetter from Dienes, Louis to Sabin, Albert B. dated 1948-05-27.Sabin Collection Fair Use Policy</a
Requests for Cultures, Slides and Other Materials -- 1935-39 -- Correspondence, Miscellaneous -- letter, 1939-06-08
No full textLetter from Dienes, Louis to Sabin, Albert B. dated 1939-06-08.Sabin Collection Fair Use Policy</a
Electronically Mediated Selectivity in Ring Opening of 1-Azirines. The 3-<i>Z</i> Mode: Convenient Route to 2-Aza-1,3-dienes
No full textReaction of 1-azirine-3-methylacrylates 1a,b with imidazoles and pyrazoles under mild conditions
results in the formation of 2-aza-1,3-dienes 2a−g containing a potential leaving group at the
1-position. Simple alcohols (methanol and ethanol) react similarly with 1a,b in the presence of
sodium carbonate to afford 2h−j. Utilization of 2 in the hetero Diels−Alder reaction with electron-deficient dienophiles is described
Ligand Control in Co-Catalyzed Regio- and Enantioselective Hydroboration: Homoallyl Secondary Boronates via Uncommon 4,3-Hydroboration of 1,3-Dienes
No full textEnantiopure homoallylic boronate esters are versatile
intermediates
because the C–B bond in these compounds can be stereospecifically
transformed into C–C, C–O, and C–N bonds. Regio-
and enantioselective synthesis of these precursors from 1,3-dienes
has few precedents in the literature. We have identified reaction
conditions and ligands for the synthesis of nearly enantiopure (er
>97:3 to >99:1) homoallylic boronate esters via a rarely seen
cobalt-catalyzed
[4,3]-hydroboration of 1,3-dienes. Monosubstituted or 2,4-disubstituted
linear dienes undergo highly efficient regio- and enantioselective
hydroboration with HBPin catalyzed by [(L*)Co]+[BARF]−, where L* is typically a chiral
bis-phosphine ligand with a narrow bite angle. Several such ligands
(e.g., i-PrDuPhos, QuinoxP*, Duanphos, and BenzP*)
that give high enantioselectivities for the [4,3]-hydroboration product
have been identified. In addition, the equally challenging problem
of regioselectivity is uniquely solved with a dibenzooxaphosphole
ligand, (R,R)-MeO-BIBOP. A cationic cobalt(I) complex
of this ligand is a very efficient (TON >960) catalyst while also
providing excellent regioselectivities (rr >98:2) and enantioselectivities
(er >98:2) for a broad range of substrates. A detailed computational
investigation of the reactions using Co complexes from two widely
different ligands (BenzP* and MeO-BIBOP) employing the B3LYP-D3 density
functional theory provides key insights into the mechanism and the
origins of selectivities. The computational results are in full agreement
with the experiments. For the complexes we have examined thus far,
the relative stabilities of the diastereomeric diene-bound complexes
[(L*)Co(η4-diene)]+ lead
to the initial diastereofacial selectivity, which in turn is retained
in the subsequent steps, providing exceptional enantioselectivity
for the reactions
- …
