N-Vinyl-1,3-oxazolidine-2-thiones as Dienophiles in Inverse Hetero-Diels-Alder Reactions: New Prospects for Asymmetric Induction

Abstract

Several N-vinyl-1,3-oxazolidine-2-thione (N-vinyl OZT) were conveniently used as new dienophiles in Eu(fod)₃-catalyzed reverse hetero-Diels-Alder reactions involving benzylidene pyruvic acid methyl ester. Simple chiral N-vinyl OZT analogues homogeneously led to moderate endo and facial diastereoselectivities, when compared to those obtained with the corresponding N-vinyl-1,3-oxazolidin-2-ones. In contrast, high diastereocontrols were ­observed with a sugar-derived N-vinyl OZT.

Key words

oxazolidinethiones - hetero-Diels-Alder - enamide

References and Notes

• 1 Gaulon C. Dhal R. Chapin T. Maisonneuve V. Dujardin G. J. Org. Chem.  2004,  69:  952 
• 3a

  OZTs can readily be transformed into oxazolines using Raney Ni^® (see ref. 3b) and further hydrolysed. Up to 74% of chemical transformation was attained on model compounds. Current explorations in our laboratory indicate possible removal of the anomeric OZT moiety through a transglycosylation reaction which will be disclosed in due time.

• 3b Gosselin G. Bergogne M.-C. de Rudder J. De Clerq E. Imbach J.-L. J. Med. Chem.  1986,  29:  203 
• 4a Girniene J. Apremont G. Tatibouët A. Sackus A. Rollin P. Tetrahedron  2004,  60:  2609 ; and references cited therein
• 4b Girniene J. Tatibouët A. Sackus A. Yang J. Holman GD. Rollin P. Carbohydr. Res.  2003,  338:  711 
• 5a Velazquez F. Olivo HF. Curr. Org. Chem.  2002,  6:  1 
• 5b Jalce G. Seck M. Franck X. Hocquemiller R. Figadère B. J. Org. Chem.  2004,  69:  3240 
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• 6 Chéry F. Desroses M. Tatibouët A. De Lucchi O. Rollin P. Tetrahedron  2003,  59:  4563 
• 7 Girniene J. Tardy S. Tatibouët A. Sackus A. Rollin P. Tetrahedron Lett.  2004,  45:  6443 
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2

Gaulon, C.; Dhal, R.; Chapin, T.; Dujardin, G. unpublished results.

9

Tardy, S.; Tatibouët, A.; Rollin, P. unpublished results.

10

Compound 8 endo I: [α]_D ²⁰ +50 (c 1.0, CHCl₃). ¹H NMR (CDCl₃): δ = 1.33, 1.36, 1.47 (3 s, 12 H, CH ₃), 1.85 (dt, J _AB = 12.8 Hz, J _{2ax ′ -3 ′} = J _{2ax ′ -1 ′} = 11.3 Hz, 1 H, H_{2ax ′}), 2.36 (ddt, J _AB = 12.8 Hz, J _{2eq ′ -3 ′} = 6.3 Hz, J _{2eq ′ -1 ′} = J _{2eq ′ -4 ′} = 1.8 Hz, 1 H, H_{2eq ′}), 3.38 (d, J _AB = 10.0 Hz, 1 H, H_7b), 3.79 (s, 3 H, H_{7 ′}), 3.80-4.00 (m, 2 H, H_6b, H_{3 ′}), 4.17-4.80 (m, 4 H, H₄, H₅, H_6a, H_7a), 4.38 (d, J _2-1 = 3.5 Hz, 1 H, H₂), 5.70 (d, J _1-2 = 3.5 Hz, 1 H, H₁), 6.20 (t, J _{4 ′ -3 ′} = J _{4 ′ -2eq ′} = 1.6 Hz, 1 H, H_{4 ′}), 6.29 (dd, J _{1 ′ -2ax ′} = 11.3 Hz, J _{1 ′ -2eq ′} = 1.8 Hz, 1 H, H_{1 ′}), 7.18-7.41 (m, 5 H, H-arom.) ppm. ¹³C NMR (CDCl₃): δ = 25.1, 26.6, 26.8, 31.1 (CH₃), 34.4 (C-2′), 38.6 (C-3′), 47.0 (C-7), 52.4 (C-7′), 68.2 (C-6), 73.2 (C-5), 77.4 (C-4), 83.5 (C-3), 83.9 (C-2), 88.3 (C-1′), 103.2 (C-1), 110.5, (CIV-iPrd), 114.4 (C-4′), 114.9 (CIV-iPrd), 127.2 (C-o′), 127.5 (C-p′), 129.1 (C-m′), 142.0 (C-n′), 144,0 (C-5′), 162.4 (C-6′), 186.8 (C=S) ppm. MS (IS): m/z = 548.5 [M + H]⁺.

11

Compound 8 endo II: [α]_D ²⁰ -26 (c 0.5, CHCl₃). ¹H NMR (CDCl₃): δ = 1.17, 1.37, 4.41, 1.62 (4 s, 12 H, CH ₃), 1.86 (dt, J _AB = 12.8 Hz, J _{2ax ′ -3 ′} = J _{2ax ′ -1 ′} = 11.3 Hz, 1 H, H_{2ax ′}), 2.37 (ddt, J _AB = 12.8 Hz, J _{2eq ′ -3 ′} = 6.5 Hz, J _{2eq ′ -1 ′} = J _{2eq ′ -4 ′} = 1.8 Hz, 1 H, H_{2eq ′}), 3.69 (d, J _AB = 10.3 Hz, 1 H, H_7b), 3.82 (s, 3 H, H_{7 ′}), 3.90-4.00 (m, 4 H, H_{3 ′}, H₅, H_7a, H_6b), 4.09 (dd, J _AB = 7.3 Hz, J _6a-5 = 2.8 Hz, 1 H, H_6a), 4.17 (d, J _4-5 = 8.5 Hz, 1 H, H₄), 4.59 (d, J _2-1 = 3.5 Hz, 1 H, H₂), 5.71 (d, J _1-2 = 3.5 Hz, 1 H, H₁), 6.21 (t, J _{4 ′ -3 ′} = J _{4 ′ -2eq ′} = 1.6 Hz, 1 H, H_{4 ′}), 6.32 (dd,
J _{1 ′ -2ax ′} = 11.3 Hz, J _{1 ′ -2eq ′} = 1.8 Hz, 1 H, H_{1 ′}), 7.18-7.40 (m, 5 H, H-arom.) ppm. ¹³C NMR (CDCl₃): δ = 25.4, 26.6, 27.0, 31.1 (CH₃), 33.7 (C-2′), 38.6 (C-3′), 46.6 (C-7), 52.5 (C-7′), 68.6 (C-6), 73.9 (C-5), 77.4 (C-4), 84.0 (C-2), 84.2 (C-3), 88.3 (C-1′), 103.2 (C-1), 110.6, (CIV-iPrd), 114.8 (C-4′, CIV-iPrd), 127.2 (C-o′), 127.5 (C-p′), 129.1 (C-m′), 142.0 (C-n′), 143.8 (C-5′), 162.4 (C-6′), 186.2 (C=S) ppm. MS (IS): m/z = 548.5 [M + H]⁺.