Complex metal hydride reduction of carbon-carbon unsaturation. I. Sodium borohydride reduction of .alpha.-phenylcinnamates and related systems

Abstract

The substituted methyl cinnamates 4 and 5 have provided a unique system for the study of various mechanistic aspects of the nucleophilic 1,4 addition of sodium borohydride to ,/3-unsaturated esters. Competitive rates of reduction for two sets of methyl a-phenyl-trores-cinnamates (4), para-substituted in the a and ß rings, respectively, correlate linearly with Hammett values. The similarity in pa (1.74) and ps (1.44) indicates that the transition state for hydride transfer occurs before significant change in geometry of the ,/3-unsaturated carbonyl system occurs. Competitive rate studies for methyl a-(para substituted phenyl)acrylates (2) and methyl of-phenyl-a's-and -trans-crotonates (14 and 15) are corroborated by the data obtained for the cinnamates.Carbon-carbon double bonds conjugated with strong anion-stabilizing groups (e.g., COR, CO2R, CN, SO2R, NO2) have occasionally been observed to undergo reduction with sodium borohydride.2-11 Although it is recognized that sodium borohydride exhibits nucleophilic behavior,3-4 little is known concerning the mechanism or even the general structural requirements for the occurrence of such reactions.

Chemistry of heterocyclic compounds. 22. Condensation reactions of 2-substituted pyridines

“…Method B. Acetic Anhydride-Triethylamine. A solution of ethyl 2-pyridylacetate (3.31 g, 20 mmol), 2-pyridinecarboxaldehyde (2.15 g, 20 mmol), triethylamine (25 ml), and acetic anhydride (25 ml) was stirred at 25 °C under nitrogen for 15 h. The mixture was poured into ice water, basified with solid sodium carbonate, and extracted with ether. The ether layer was dried over anhydrous sodium sulfate and concentrated.…”

Synthesis of oxidized metabolites of dibenz[a,c]anthracene

“…Direct dehydrogenation with DDQ8 afforded 7 in moderate but variable yield, and substantial further conversion to 1 also took place. Reaction of 4 with lead tetraacetate failed to furnish 7, despite the fact that analogous reaction of 7,8,9,10-tetrahydrobenzo[a]pyrene provides the most convenient route to 7,8-dihydrobenzo[a]pyrene.4b'9 Bromination of 4 with NBS gave the bromo derivative 5.…”

Inhibition of β-Lactamases by Monocyclic Acyl Phosph(on)ates

“…The product, purified by distillation (bp 165-167°C, 0.3 Torr), proved to be a mixture of the E and (required) Z isomers, where the latter comprised some 70% of the total. 1 The E and Z isomers were distinguishable because of the upfield anisotropic shift of the vinyl proton of the latter caused by the adjacent (cis) phenyl ring (18,19). Attempts to separate these isomers by fractional distillation or by silica gel chromatography were unsuccessful, so the mixture was carried forward.…”