Catalytic Enantioselective Decarboxylative Allylations of a Mixture of Allyl Carbonates and Allyl Esters: Total Synthesis of (−)‐ and (+)‐Folicanthine

Abstract

A highly enantioselective decarboxylative allylation of a mixture of enol carbonates and allyl esters has been achieved. The strategic viability of this methodology has been demonstrated through the total synthesis of cyclotryptamine alkaloids (-)- and (+)-folicanthine (1 a) and the formal total synthesis of (-)-chimonanthine (1 b), (+)-calycanthine (1 c), and (-)-ditryptophenaline (1 d).

Palladium‐Catalyzed Asymmetric Decarboxylative Allylation of Azlactone Enol Carbonates: Fast Access to Enantioenriched α‐Allyl Quaternary Amino Acids

“…When a 1:1 mixture of allyl enol carbonates 2a and 2bs were reacted in the presence of our chiral catalytic system, we isolated only an equimolar amount of the enantioenriched allylated 3a and methallylated 3bs compounds, with the lack of any scrambling products (Scheme ). This evidence supports the hypothesis that the allylation proceeds via a tight ion pair intramolecular process …”

Synthesis of 2-oxindoles via 'transition-metal-free' intramolecular dehydrogenative coupling (IDC) of sp2 C–H and sp3 C–H bonds

“…X-ray crystal structure determination of (±)- 19b proved the outcome of the reaction unambiguously. It was noteworthy to observe Pd-catalyzed highly enantio-, chemo-, and diastereoselective double decarboxylative allylations on dimeric β- N -arylamido allyl ester 19c to yield the enantiopure compounds of type 20a and b in good yields [ 78 – 81 ]. Especially, enantioenriched 20b is the advanced intermediate for the total syntheses of 3a,3a'-bispyrrolo[2,3- b ]indole alkaloids, chimonanthine ( 22a ), folicanthine ( 22b ), and their rearranged skeleton such as calycanthine ( 22c ) ( Scheme 5 ) [ 78 ].…”

Recent Advances in Natural Products Synthesis Using Bifunctional Organocatalysts Bearing a Hydrogen‐Bonding Donor Moiety

“…Introduction of suitable protecting groups enabled conversion to 48 without affecting the enantioselectivity. Diastereoselective decarboxylative allylation of 48 was then carried out with allylcarbonate 50 in the presence of palladium catalyst with the Trost ligand 51 to give 52 as the major diastereomer . After removal of the silyloxymethyl group in 52 , the resulting oxindole 53 was subjected to a second diastereoselective decarboxylative allylation via allylchloroformate 54 to give 55 , which contains the two contiguous all‐carbon quaternary stereogenic centers of 57 .…”

“…After removal of the silyloxymethyl group in 52 , the resulting oxindole 53 was subjected to a second diastereoselective decarboxylative allylation via allylchloroformate 54 to give 55 , which contains the two contiguous all‐carbon quaternary stereogenic centers of 57 . After conversion of the Boc group in 55 to a methyl group, the allyl group was oxidatively converted into a formyl group to give 56 , which is a known key synthetic intermediate for (+)‐folicanthine ( 57 ) …”

“…Similarly, N ‐Bn derivative 67 was also obtained in 86% yield with 92% ee from the corresponding sulfonyl oxindole. From the adduct 61 , a synthetic key intermediate 66 for (−)‐folicanthine ( 57 ) was synthesized via diastereoselective α‐alkylation of oxindole 63 with ethyl bromoacetate ( 64 ). Other dimeric HPIs, (−)‐chimonanthine ( 68 ) and (+)‐calycanthine ( 69 ), were also synthesized from 67 …”