Enantioselective synthesis of a potential key intermediate for the total synthesis of fumagillin

Copper-Catalyzed Reductive Ireland–Claisen Rearrangements of Propargylic Acrylates and Allylic Allenoates

“…It should also be noted that boron enolates reported for the Ireland-Claisen rearrangements in the prior literature were almost exclusively enolborinate derivatives, whereas this reductive methodology generates enolborates for rearrangements. Although boron dienolates have been prepared and applied to numerous vinylogous aldol reactions, − the only application to an Ireland-Claisen rearrangement was in the context of the synthesis of elemene 52 , where Corey induced the asymmetric Claisen rearrangement of ester 49 using a stoichiometric amount of chiral bromoborane 50 , yielding 51 in 85% yield with low dr but high ee for the major diastereomer (Figure ). …”

Large‐Ring Carbocycles

“…Watson and co-workers recently employed a ring-closing metathesis strategy using a chiral auxiliary to enantioselectively construct the cyclohexene core of fumagillin. 100 Diene 173, where R = H, when subjected to ring-closing metathesis using 5 mol % of 3 in dichloromethane, provided the corresponding carbocyclic ring 174 in 88% yield as a single enantiomer. Interestingly, diene 175, where R = Ph, failed to undergo ring-closing metathesis.…”

Enantio- and Diastereoselective Synthesis of syn-β-Hydroxy-α-vinyl Carboxylic Esters via Reductive Aldol Reactions of Ethyl Allenecarboxylate with 10-TMS-9-Borabicyclo[3.3.2]decane and DFT Analysis of the Hydroboration Pathway

“…Both enantiomers of syn -β-hydroxy-α-vinyl imides 5 can be obtained by using enantioselective aldol reactions of chiral crotonate imides (Figure ). Evans’ chiral N -acyl oxazolidinones are widely applied for this purpose, but other methods include use of Oppolzer’s chiral sultam and Crimmins’ chiral oxazolidinethione reagents . Here we report the development of an enantio- and diastereoselective synthesis of syn -β-hydroxy-α-vinyl carboxylate esters 3 via aldol reactions of aldehydes with ( Z )-dienolborinate Z -(O)-8a that is generated in situ from the hydroboration of allenyl ester 2 with 10-trimethylsilyl-9-borabycyclo[3.3.2]decane ( 1R , also known as 10-TMS-9-BBD-H, and as the Soderquist borane). , Density functional theory (DFT) calculations indicate that Z -(O)-8a is generated by a kinetically controlled 1,4-hydroboration reaction pathway.…”