Keten. Part 15. Reactions of diphenylketen with some N-alkyl nitrones

Abstract

By Anthony F. Gettins, David P. Stokes, Giles A. Taylor," and (in part) Christopher B. Judge, Department N-(Fluoren-9-ylidene)alkylamine N-oxides ( I ) react with diphenylketen to give spiro-oxazolidinones ( 2 ) and spiro-azetidinones (1 3). The adduct (2d) dissociates thermally to give the ylide ( 9 ) . The N-oxides (1) behave like normal nitrones in cycloaddition reactions with dipolarophiles.

XY–ZH systems as potential 1,3-dipoles. Part 12. Mechanism of formation of azomethine ylides via the decarboxylative route from α-amino acids

“…( 8) e (9), promoted by the ability of R in (8) to delocalise negative charge. This suggestion would seemingly accord with the observation that tetrahydroisoquinoline-1 -carboxylic acid (20), in which the carboxy group is in a benzylic site, reacts (DMF, 120 "C, 1 h) with benzaldehyde and N-methylmaleimide to give a 1.2: 1.7: 1.0: 1.9 mixture of (21a)-(24a),' i.e., a 1: 1 ratio of adducts derived from anti-(25a)-and sjw-( 26)-dipoles.…”

“…1 755, 1 680 (amide), 750,740, and 690 cm-'; 6 2.86 (1 H, m, lla-H), 2.96-3.04 (1 H, m, llP-H), 3.01 (3 H, s, 2-Me), 3.17(1 H,dd, J 4 a n d 16Hz, lla-H),3.24(1 H,dd, J 7 a n d 9 H z , 4-H), 3.27 ( 1 H,d,J 15 Hz,3.363.43 (2 H,m,4.07 (1 H,d,J15Hz,6-H),6.29(1H,dd,J9and16Hz, olefinic-H), 6.73 (1 H,d,J 16 Hz,m,ArH) (20). and 104 (33).…”

“…178-180°C (Found: C, 76.9; H, 6.05; N, 7.8); vmax. 1 755, 1 685 (amide), 745, and 690 cm-'; 6 2.65 (1 H, m, lla-H), 3.01 (3 H,s,2-Me), 3.00(1 H,m, lla-H),3.10(1 H, t, J8Hz,4-H),3.18(1 H,t,J9Hz, llb-H),3.29(lH,dd,J8and9 Hz, 3a-H), 3.33-3.38 (2 H, m, 1lp-and 6-H), 4.07 (1 H,d,J 15 Hz,6.26 ( 1 H, dd, J 8 and 16 Hz, olefinic-H), 6.76 (1 H,d,J 16 Hz,m,ArH); 'H NOEDSY (x): irradiation of lla-H caused enhancement of 3a-H ( O S ) , llb-H (2), and 4-H ( 5); irradiation of llb-H caused enhancement of lla-H (2); m/z (%) 358 (M', 29), 267 (loo), 247 (20). and 104 (33).…”

Pericyclic Cascade with Chirality Transfer: Reaction Pathway and Origin of Enantioselectivity of the Hetero‐Claisen Approach to Oxindoles

“…[9] Building upon this precedent, and the utility of 3-alkyl-3-aryloxindoles ( 3 ) as valuable synthetic intermediates that can be derivatized to numerous natural products and medicinal targets, [10] we reported [6] that treatment of nitrone 1a , derived from Garner’s aldehyde, [11] with an alkylarylketene ( 2 ) afforded, after aqueous workup, oxindoles ( S )- 3a – c in 80–88% yield and 81–90% ee (Table 1, entries 1–3). Further experimental optimization of this process showed that nitrones derived from Garner’s aldehyde are critical to achieve high asymmetric induction, with increasing size of the oxazolidine N -substituent ( 1b – c ) consistently leading to improved enantio-selectivities.…”

“…The initially proposed reaction pathways for this process (pathway I, Scheme 1), [6–9] involved the ketene (shown here as 2a ) reacting as an electrophile towards the nitrone (shown here as 4 ), giving, after rearomatization, the experimentally isolable imino acids 5 bearing a quaternary carbon. Subsequent hydrolysis and cyclization afford the oxindole products 3 .…”