Synthesis of the C(26)-C(42) and C(43)-C(67) pyran-containing fragments of amphidinol 3 via a common pyran intermediate

The pyran-containing fragments 1 and 2 of AM3 have been synthesized from the common pyran intermediate 3. Careful orchestration of the alcohol protecting groups was necessary to facilitate deprotection of alcohol functionality in the presence of the chemically sensitive polyene chain.     

Total synthesis of +-superstolide A

A convergent and highly stereocontrolled synthesis of +-superstolide A (1) has been accomplished. Key steps of this synthesis include the intramolecular Suzuki reaction of 26 and the highly diastereoselective transannular Diels-Alder cyclization of macrocyclic octaene 3.     

Total syntheses of (+)-tedanolide and (+)-13-deoxytedanolide

Convergent total syntheses of the potent cytotoxins (+)-tedanolide (1) and (+)-13-deoxytedanolide (2) are described. The carbon framework of these compounds was assembled via a stereoselective aldol reaction that unifies the C(1)-C(12) ketone fragment 5 with a C(13)-C(23) aldehyde fragment 6 (for 13-deoxytedanolide) or 52 (for tedanolide). Multiple obstacles were encountered en route to (+)-1 and (+)-2 that required very careful selection and orchestration of the stereochemistry and functionality of key intermediates. Chief among these issues was the remarkable stability and lack of reactivity of hemiketals 33b and 34 that prevented the tedanolide synthesis from being completed from aldol 4. Key to the successful completion of the tedanolide synthesis was the observation that the 13-deoxy hemiketal 36 could be oxidized to C(11,15)-diketone 38 en route to 13-deoxytedanolide. This led to the decision to pursue the tedanolide synthesis via C(15)-(S)-epimers, since this stereochemical change would destabilize the hemiketal that plagued the attempted synthesis of tedanolide via C(15)-(R) intermediates. However, use of C(15)-(S)-configured intermediates required that the side-chain epoxide be introduced very late in the synthesis, owing to the ease with which the C(15)-(S)-OH cyclized onto the epoxide of intermediate 50.     

Enantio- and diastereoselective synthesis of syn-beta-hydroxyallylsilanes via a chiral (Z)-gamma-silylallylboronate

syn-beta-Hydroxyallylsilanes of general structure 11 and 28 are prepared in 50-86% yield and 91-95% ee (for aliphatic aldehydes; 50% ee for benzaldehyde) via the BF(3).Et(2)O-promoted gamma-silylallylboration reactions, using reagents 14 and 15.     

Synthesis of 2-epi-amphidinolide E: an unexpected and highly selective C(2)inversion during an esterification reaction

A synthesis of 2-epi-amphidinolide E (1) has been accomplished via an unexpected and highly diastereoselective C(2) stereochemical inversion during the modified Yamaguchi esterification of alcohol 4b and Fe(CO)3-complexed dienoic acid 7. [reaction: see text].     

Total Synthesis of Amphidinolide E and Amphidinolide E Stereoisomers

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 stereocenter 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.     

Total Synthesis of (−)-Bafilomycin A1: Application of Diastereoselective Crotylboration and Methyl Ketone Aldol Reactions

A careful orchestration of protecting groups is an essential requirement for the total synthesis of the macrolide antibiotic bafilomycin A₁ ( 1 ). Key steps were the Suzuki cross-coupling reaction of two advanced, suitably protected intermediates prior to closure of the macrocycle, as well as a highly stereoselective methyl ketone aldol reaction.     

Studies on the synthesis of quartromicins a(3) and d(3): synthesis of the vertical and horizontal bis-spirotetronate fragments

Syntheses of the vertical (3) and horizontal (4) bis-spirotetronate units of quartromicins A3 and D3 are described, along with an efficient synthesis of alpha-hydroxy aldehyde exo-8b, a precursor to the exo-spirotetronate fragments 19 and 21.     

Enantioselective synthesis of (+)-crocacin C. An example of a highly challenging mismatched double asymmetric δ-stannylcrotylboration reaction

A concise, enantioselective synthesis of (+)-crocacin C is described, featuring a highly diastereoselective mismatched double asymmetric δ-stannylcrotylboration of the stereochemically demanding chiral aldehyde 9 with the bifunctional crotylborane reagent (S)-E-10. The total synthesis of (+)-crocacin C was accomplished in seven steps (longest linear sequence) starting from commercially available precursors.