Synlett 2010(4): 664-666  
DOI: 10.1055/s-0029-1219348
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Probing the Effect of Allylic Substitution on Cyclic Ammonium Ylid Rearrangements

Julien Sançon, J. B. Sweeney*
Department of Chemistry, University of Reading, Reading RG6 6AD, UK
Fax: +44(118)3786121; e-Mail: j.b.sweeney@reading.ac.uk;
Weitere Informationen

Publikationsverlauf

Received 11 January 2010
Publikationsdatum:
25. Januar 2010 (online)

Abstract

The [2,3]-sigmatropic rearrangement of tetrahydropyridine-derived ammonium ylids is a valuable method for the preparation of substituted pyrrolidine carboxylates. The presence of an allylic substituent does not intrinsically reduce the yield of rearrangements, and the diastereoselectivity of rearrangement is related to the structure of the diazo reactant. The method represents a very rapid means of accessing complex pyrrolidines, as shown by preparation of a precursor to the core of lactacystin.

13

Key Data
¹H NMR (400 MHz, CDCl3): δ = 2.28 (3 H, s), 2.28-2.35
(1 H, m), 2.35-2.41 (1 H, m), 2.60-2.70 (1 H, m), 2.75-2.85 (1 H, m), 2.90 (1 H, d), 2.90 (1 H, d), 3.50-3.57 (1 H, br m), 3.70 (3 H, s), 5.20-5.28 (1 H, m), 5.73-5.81 (1 H, m). ¹³C NMR (100 MHz, CDCl3): δ = 39.0, 41.3, 42.6, 52.4, 55.1, 65.2, 72.3, 128.8 , 135.5, 172.3. MS (CI+): m/z (%) = 182(100) [MH+], 122(75), 79, 49. HRMS: m/z calcd for C10H15NO2: 182.1182; found: 182.1181.

16

Prepared from methyl 4-methyl-3-oxopentanote and trisyl azide (MeCN, Et3N, r.t. 20 h).
Key Data R f = 0.29 (PE-EtOAc, 9:1): Anal. Calcd (%) for C7H10N2O3: C, 49.41; H, 5.92; N, 16.46. Found: C, 49.39; H, 6.20; N, 16.33. IR (neat): νmax = 2976, 2874, 2130, 1725, 1658, 1437, 1308 cm. ¹H NMR (250 MHz, CDCl3): δ = 1.15 [6 H, d,
J = 6.8 Hz, CH(CH 3)2], 3.59 [1 H, sept, J = 6.8 Hz, CH(CH3)2], 3.85 (2 H, s, OCH3). ¹³C NMR (62.5 MHz, CDCl3): δ = 18.9 (2 × CH3), 37.2 [CH(CH3)2], 52.5 (OCH3), 53.8 (CN2), 162.0 (CO2), 197.3 (CO). MS (CI+): m/z (%) = 171.1 (80) [MH+], 145.1 (100). HRMS: m/z calcd for C7H10N2O3: 171.0770; found: 171.0771.

17

The relative stereochemistry of cis- and trans- 10 was deduced from NOE experiments (alkene methine-ring methyl interactions), which will be reported elsewhere in due course.

18

The necessary analytical experiments to rigorously confirm these structural deductions are currently in progress.