silyl Acetal 7-Atom Tether Ring eader. J. C. Tetrahedron Lett. 19 170°c COMe CO,Me Note: Intermolecular variant gives a mixture of 4 diastereomers Craig, D. Reader, J C. Tetrahedron Lett. 1992, 33, 6165 Type ll Diels-Alder To Form 8-Atom Tether Ring H 5-200 H 1 isomer Longer Tether Pn however COMe hea, K. J: Staab A J. Zandi, K. S. Tetrahedron Lett. 1991. 32, 2715. 33A-073/149611:27PMO O Si Me Ph Ph CO2Me R O O Si H H R CO2Me Me Ph Ph O O Si Me Ph Ph CO2Me Me O O Si H H Me CO2Me Me Ph Ph Me Me O O Si H H Me CO2Me Me Ph Ph Me Si O R2 R1 O Me Me Si O O R1 R2 Me Me O Si O O O Ph Ph O Si O O O Ph Ph Me CO2Me H CO2Me O Si O O O Ph Ph 160 - 170 °C R = H 64% R = Me 100% 1 isomer Silyl Acetal 7-Atom Tether Ring: H O Si O O O 170 °C 94% Craig, D.; Reader, J. C. Tetrahedron Lett. 1992, 33, 6165. Craig, D.; Reader, J. C. Tetrahedron Lett. 1990, 31, 6585. Craig, D.; Reader, J. C. Tetrahedron Lett. 1992, 33, 4073. 1:1 mixture of diastereomers Note: Intermolecular variant gives a mixture of 4 diastereomers. 1 : 1 Ph Ph 1 isomer 115 - 200 °C Me + R1 R2 Yield H O Si O H Me H H Me CN H H Me Ph Me Pr Longer Tethers: 98% 88% 78% 93% 65% 53% Ph Ph 1 isomer 80 °C 90% Me Shea, K. J.; Staab, A. J.; Zandi, K. S. Tetrahedron Lett. 1991, 32, 2715. O O Type II Diels-Alder To Form 8-Atom Tether Ring: however: + 70 : 30 33A-07 3/14/96 11:27 PM