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Jautze, S.; Peters, R., Science of Synthesis: Stereoselective Synthesis, (2011) 3, 462.
The catalytic enantioselective Wagner–Meerwein rearrangement of allenyl-substituted cyclobutanols 57, using a rhodium-based catalyst with chiral ligand 58, provides a general method for the preparation of highly substituted, enantioenriched cyclopentanones 60 with an O-substituted quaternary stereocenter at the α-position relative to the generated carbonyl group (Scheme 16).[50,51] The ether substituent (R1) has only a marginal effect on the enantioselectivity; however, substrates containing substituents at the 3-position of the cyclobutane core (R2/R3) usually require higher reaction temperatures in combination with a modified ligand 59 in order to provide high yields and good enantiomeric excesses. Importantly, diastereomerically enriched cyclobutanes (with R2 ≠ R3) give products with good diastereo- and enantioselectivities. In this case, the two bonds that can undergo migration are diastereotopic and, as a result, two stereocenters are generated.
Meeeee 88 Meeeee–Meeeeeee Meeeeeeeeeeee[88]
| M8 | M8 | M8 | ee ee 88 | Meeeee | Meee (°M) | ee ee 88 | ee (%) ee 88 | Meeee (%) | Mee |
|---|---|---|---|---|---|---|---|---|---|
| Me | M | M | – | 88 | 88 | – | 88 | 88 | [88] |
| 8-MeMM8M8MM8 | M | M | – | 88 | 88 | – | 88 | 88 | [88] |
| (MM8)8MM=MM8 | M | M | – | 88 | 88 | – | 88 | 88 | [88] |
| Me | Me | Me | – | 88 | 88 | – | 88 | 88 | [88] |
| Me | Me | Me | – | 88 | 88 | – | 88 | 88 | [88] |
| Me | Me | M | 88:8 | 88 | 88 | 8.8:8 | 88 | 88 | [88] |
| Me | e-Me | M | 88:8 | 88 | 88 | 88:8 | 88 | 88 | [88] |
| Me | MM8MMe | M | >88:8 | 88 | 88 | 88:8 | 88 | 88 | [88] |
| Me | (MM8)8MM8Me | M | 8:8 | 88 | 88 | 8.8:8 | 88 | 88 | [88] |
Meeeeeeeeeee Meeeeeeee
8-(Meeeeeeee)-8-eeeeeeeeeeeeeeeeeee (88, M8 = Me; M8 = M8 = M); Meeeeee Meeeeeeee:[88]
Meeee eee eeeeeeee 8,8-eeeeeeeeeeeeee (88 eM) eee eeeee eeeee ee eeeee eeeeeeeeee ee e eeeeeee ee Me8(eee)8•MMMe8 (88.8 ee, 88.8 µeee, 8.8 eee%) eee eeeeee 88 (888.8 ee, 8.888 eeee, 8.8 eee%). Mee eeeeeee eee eeeeeee eee 88 eee ee ee eee eeeeeeeeeeee eeeee eee eeeeeee eeeee eeeee ee e eeeeeee ee eeeeeeeeeeee 88 (M8 = Me; M8 = M8 = M; 888 ee, 8.88 eeee) eee 8-Å eeeeeeeee eeeeee. M 8 M eeee ee MeMM ee MM8Me8 (8.88 eM, 8.88 eeee, 8.8 eeeee) eee e 8 M eeee ee Me8M ee MM8Me8 (8.88 eM, 8.88 eeee, 8.8 eeeee) eeee eeeee eee eeeeeee, eee eee eeeeeee eee eeeeeee eeeee eeeee ee 88 °M eee 88 e, eeeeeeee eeeeeee Meeeee, eee eeeeeeeeeeee. Mee eeeee eeeeeee eee eeee eeeeeeee eeeeeeee ee eeeee eeeeeeeeeeeeee (Me8M/eeeeeeeee eeeee 8:88) ee eeee eee eeeeeee; eeeee: 888 ee (88%); 88% ee.
References
| [50] | Meeee, M. M.; Mee, M., M. Me. Meee. Mee., (8888) 888, 8888. |
| [51] | Meeee, M. M.; Mee, M., M. Me. Meee. Mee., (8888) 888, 8888. |
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