2003
DOI: 10.1021/jo026671s
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Correlation between pKa and Reactivity of Quinuclidine-Based Catalysts in the Baylis−Hillman Reaction:  Discovery of Quinuclidine as Optimum Catalyst Leading to Substantial Enhancement of Scope

Abstract: The reactivity of a variety of quinuclidine-based catalysts in the Baylis-Hillman reaction has been examined, and a straightforward correlation between the basicity of the base and reactivity has been established, without exception. The following order of reactivity was established with pK(a)'s of the conjugate acids (measured in water) given in parentheses: quinuclidine (11.3), 3-hydroxyquinuclidine (9.9), DABCO (8.7), 3-acetoxyquinuclidine (9.3), 3-chloroquinuclidine (8.9), and quinuclidinone (7.2). The high… Show more

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Cited by 227 publications
(119 citation statements)
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“…These compounds are of interest as antiinfectives, but nothing is known structurally about how they might act. The 3-OH quinuclidine pK a is expected to be ∼10-11 (23), so these compounds are likely to bind to SQS as cationic (ammonium) species, and it seemed possible that, as with, e.g., nitrogen-containing bisphosphonate inhibitors of FPPS (24,25), they might mimic the transition statereactive intermediates involved in PSPP (or squalene-dehydrosqualene) formation. Although BPH-651 is only a modest CrtM inhibitor (K i ¼ 17.5 μM), we were able to obtain the structure of a CrtM/BPH-651 complex (full crystallographic details are given in Table S3), as well as that of a second ammonium-contain- ing species (26) BPH-673 (Table S3), a potent SQS inhibitor which has a K i ∼ 2 μM for CrtM inhibition.…”
Section: Resultsmentioning
confidence: 99%
“…These compounds are of interest as antiinfectives, but nothing is known structurally about how they might act. The 3-OH quinuclidine pK a is expected to be ∼10-11 (23), so these compounds are likely to bind to SQS as cationic (ammonium) species, and it seemed possible that, as with, e.g., nitrogen-containing bisphosphonate inhibitors of FPPS (24,25), they might mimic the transition statereactive intermediates involved in PSPP (or squalene-dehydrosqualene) formation. Although BPH-651 is only a modest CrtM inhibitor (K i ¼ 17.5 μM), we were able to obtain the structure of a CrtM/BPH-651 complex (full crystallographic details are given in Table S3), as well as that of a second ammonium-contain- ing species (26) BPH-673 (Table S3), a potent SQS inhibitor which has a K i ∼ 2 μM for CrtM inhibition.…”
Section: Resultsmentioning
confidence: 99%
“…[24] While such correlations hold within a narrow class of compounds, they cannot be used for the comparison of different classes of compounds. With pK aH values of 7.61 (Ph 3 P) and 9.96 (MePh 2 P) tertiary phosphanes are considerably weaker Brønsted bases in acetonitrile than pyridine 1 b (pK aH = 12.53) and DMAP (1 f; pK aH = 17.95).…”
Section: Resultsmentioning
confidence: 99%
“…[102] Eine zweite Strategie nutzt Lewis- Tabelle 4). [103] Die Autoren wiesen ausdrücklich auf einen Unterschied zu früheren Studien hin: Dort war kein Zusammenhang zwischen dem pK S -Wert und der Geschwindigkeit gefunden worden, weil pK S -Werte aus Messungen in Wasser verwendet wurden. [104] Mit den in DMSO bestimmten pK S -Werten war dagegen ein eindeutiger Zusammenhang erkennbar.…”
unclassified