Enantioselective synthesis of an advanced intermediate to quassinoids

✍ Scribed by Claude Spino; Noah Tu

• Publisher: Elsevier Science
• Year: 1994
• Tongue: French
• Weight: 276 KB
• Volume: 35
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(00)73071-1

✦ Synopsis

We have recently communicated our results on a novel strategy to etficiently and stereoselectively construct the quassinoid framework via a Diene-Transmissive Diels-Alder strategy (Eq l).l Although both the hetero-and intramolecular Diels-Alders proceeded with complete endo-selectivity, the stereochemistry at Ct4.16 directed the intramolecular cycloaddition mostly to the undesired face of the molecule. We now have prepared an enantiomerically pure tetracyclic intermediate demonstrating the ability of a methyl group at C4 and a t-butyldimettiylsilyloxy group at C3 (steroid numbering) to control the absolute configuration at Cs, cd.

C7, and Cl0 in the intramolecular cycloaddition,2 and in fact reverse the effect of the C14.16 stueocenters.

Since we have described earlier a method to control the abaOlUte stereochemistry at C14,16,~ we can now formally obtain the desired absolute stereochemistry at all newly created chiral centers in these sequential cycloadditions.