Regard, they applied bifunctional O cinchona alkaloid-based catalysts 21OH themol ) inRegard, they applied bifunctional

May 31, 2022

Regard, they applied bifunctional O cinchona alkaloid-based catalysts 21OH themol ) in
Regard, they applied bifunctional O cinchona alkaloid-based catalysts 21OH themol ) in (ten presence of carboxylic acids (Scheme 6) [35]. OH Ar = naphthyl O O They proposed an activation mechanism, in which the silyl dienolate is activated by the Ar Ar 9 O TMSO OTMS O O OH protonated quinuclidine, although the thiourea moiety activates the aldehyde by H-bond + neat, (LUMO) lowering. By employing this optimized Ar H MeO unoccupied molecular orbital r.t., 24 h lowest MeO Ar + Ar O OMe 15 11 up to 94 yield 14 inside the reactions 16 new catalyst, they =obtained great yields and selectivities amongst Ar e–poor (1.three eq.) as much as 56 ee as much as 60 ee 2-(trimethylsilyloxy)furan (20) and diverse aldehydes five. It is worth mentioning that each O aromatic and aliphatic substitutions O OH CN tolerated. O OH had been properly O O O OH OMeO NO2 39 yield, 54 ee 46 yield, 56 ee 32 yield, 65 ee (at 0 ) MeO MeOPhNOOOMe30 yield, 60 eeMolecules 2021, 26,Molecules 2021, 26, x FOR PEER Overview(a)the exclusive formation with the aldol item 14 in moderate yields and ees (Scheme 4a). Interestingly, the reaction with electron-poor benzaldehydes 15 yielded a mixture of the anticipated aldol-product 14 along with a cyclized dihydro-pyrone 16 in overall superior yields and moderate enantioselectivities as much as 56 ee and 60 ee, respectively (Scheme 4b). The formation of the unexpected side solution was traced back to a hetero-Diels lder reaction of 21 five (HDA), providing rise to the formation of an option pyrone regio-isomer when compared with the a single normally obtained by the reaction of Brassard’s diene with aldehydes [33].O H-bond donorcatalysts 13 (10 mol )5 ofTMSO MeOOTMSAr H neat, -20 , 24-72 h In 2007, Mukaiyama et al. presented the firstMeO employmentAr a chiral Lewis base orof 11 12 up to 42 yield 14 –rich (1.3 eq.) Ar Ph, e ganoAzoxystrobin Anti-infection catalyst 18 in=a VMAR (Scheme 5) [34]. Their investigation showed that the reaction of 4up to 65 ee substituted 2-(trimethylsiloxy)furans 17 with distinct aldehydes five at low temperatures (b) (-78 ) provided fantastic yields Ar Arto 97 ) and enantioselectivities (as much as 97 ee), even though (up O OH with just the diastereoselectivity was moderate (ten mol ) a handful of exceptions. O TMSO MeO OTMS O OH Ar = naphthyl O Ar Ar 9 O O+OOOH+11 (1.3 eq.) O O OHArHOTMSO OH O Ar R2 OHMolecules 2021, 26, x FOR PEER REVIEW15 O Ar = e–poor+18 Oneat, r.t., 24 h (10 mol ) MeO Rup to 94 yield+ArOOMeRHO ODCM, -78 , 1 h up to 97 yield up to 99:1 d.r.CN O14 H R1 up to 56 ee O OH syn-16 as much as 60 ee O5 ofOHand poor aldehydes by Scettri etet al. [30,33]. Ph and poor aldehydes by Scettri al. [30,33].88:12 d.r. 76 ee 93:7 d.r. 93 ee 78:22 d.r. OTMS 97 ee O OPh MeO MeO In 2007, Mukaiyama et al. presented the initial employment of a chiral Lewis base orO OMe O O O O NO2 CF ganocatalyst 18 within a VMAR (Scheme 5) [34]. Their study 3showed that the .reaction of 4OPh HOPh 32 yield, 65 ee substituted 2-(trimethylsiloxy)furans 17 with different0aldehydes 5 at yield, 60 ee low temperatures O 39 yield, 54 ee O O O (at ) 46 yield, 56 ee H 30 N H H H H O Me (-78 ) offered very good Me yields (up toMe 97 ) and enantioselectivities (up to 97 ee), although F C SchemeOH Asymmetric organocatalyzed VMAR reaction between Chan’s diene and and electron-rich Scheme 4. Asymmetric organocatalyzed VMAR reaction3between Chan’s diene electron-rich four. OH OH OH tBu the diastereoselectivity was moderate with just some exceptions. H Ph PhMeOup to 97 ee NO99:1 d.r. 85 ee 18 (ten mol ) up to 97 yield up to 99:1 d.r.1.