A new protocol for regio- and stereocontrolled aldol reactions through the conjugate addition of dialkylboranes to .alpha.,.beta.-unsaturated ketones

Continuous-flow processes for the catalytic partial hydrogenation reaction of alkynes

“…Both compounds were hydrogenated using the Pd@Monobor monolithic catalyst under mild conditions with >91% ene selectivity, and cis selectivity of 96% and 50%, respectively, at conversions higher than 90% (Table 2, entries 24, 25) [136]. Comparable selectivity results were obtained in batch using the Lindlar catalysts [174–175], Pd onto pumice [176] or onto nitrogen-doped carbon nanofibers [177], in the presence of 2.5–30% amine additives.…”

Generation of Stereochemically Defined Tetrasubstituted Enolborinates by 1,4‐Hydroboration of α,β‐Unsaturated Morpholine Carboxamides with (Diisopinocampheyl)borane

“…[5–8] Noteworthy among these, a highly stereoselective carbocupration of chiral ynamides followed by oxidation of the resultant vinylcuprate has been developed by Marek and co-workers.. [8] Nevertheless, the development of a simple, highly stereocontrolled method for synthesis of stereochemically defined tetrasubstituted enolates from readily available achiral starting materials remains an important objective. Toward this end, we report herein a simple procedure by which stereodefined tetrasubstituted enolborinates are generated with exceptional stereoselectivity via 1,4-hydroboration reactions [9,10] of unsaturated morpholine carboxamides with (diisopinocampheyl)borane ((Ipc) 2 BH), and demonstrate that the tetrasubstituted enolborinates undergo highly enantio- and diastereoselective aldol reactions with representative achiral aldehydes.…”

“…and 96–98% ee). By virtue of transition state TS-I proposed for the 1,4-hydroboration reaction, [9,12] we anticipated that this procedure could be used to generate stereodefined tetrasubstituted enolborinates 5 from substituted α,β-unsaturated amides 4 . Subsequent aldol reactions of enolborinates 5 should faithfully relay the enolborinate geometry to the all-carbon quaternary stereocenter in 6 via transition state TS-II .…”

“…Subsequent aldol reactions of enolborinates 5 should faithfully relay the enolborinate geometry to the all-carbon quaternary stereocenter in 6 via transition state TS-II . [2] To the best of our knowledge, stereodefined tetrasubstituted enolates have not been successfully generated with high stereochemical control by using alternative reductive aldol procedures, [9,10,12,13] but several have been generated by 1,4-addition of organometallic reagents to unsaturated carbonyl derivatives. [5m,q,r,14] …”

“…[9b,19] The results presented in Schemes 3 and 4 demonstrate that enolborinates Z (O)- 11 (from 10 , Scheme 3) and E (O)- 14 (from 13 , Scheme 4) are configurationally stable and do not isomerize via reversible formation of a C-boryl species (not shown), under the conditions of the hydroboration or the subsequent aldol reactions. The kinetic stability of these enolborinates [20] undoubtedly reflects the increase in nonbonded steric interactions that must develop in the (unobserved) O- to C- 1,3-boratropic isomerization reaction.…”