Total synthesis of amphidinolide E and amphidinolide E stereoisomers
摘要:
Four amphidinolide E stereoisomers, amphidinolide E (1), 2-epi-amphidinolide E (2), 19-epi-amphidinolide E (3), and 2-epi-19-epi- amphidinolide E (4), have been synthesized via the judicious union of aldehyde 5, allylsilanes 7 or 8, acids 9 or 10, and vinylstannane 6. The C19 stereocenters of the C19 epimeric allylsilanes 7 and 8 were introduced via crotylboration reactions early in the synthesis. [3+2] Annulation reactions of aldehyde 5 with allylsilanes 7 and 8 were employed to set the core tetrahydrofuran units of 1-4. Finally, the C2 stereo-center was installed by esterification using acid 9, without incident, or with acid 10, in which case an unexpected and completely stereoselective inversion of C2 occurs. (C) 2007 Elsevier Ltd. All rights reserved.
Regio- and stereo-selective synthesis of vinylstannanes. Transition-metal catalyzed stannylmetalation of acetylenes and conversion of enol triflates and vinyl iodides into vinylstannanes
Two new methods for the regio- and stereo-selective synthesis of vinylstannanes are described. (i) The reaction of terminal acetylenes with n-Bu3SnMgMe, n-Bu3SnAlEt2, or (n-Bu3Sn)2Zn in the presence of various transition-metal catalysts provides vinylstannanes in good yields. Whereas copper-catalyzed stannylmagnesation of 4-benzyloxy-1-butyne gives (E)-4-benzyloxy-1-tributylstannyl-1-butene exclusively