Synthesis of the B-ring of FR182877. Investigation of the reactions of 6-fumaryl 1,3,8-nonatrienes

Intramolecular Cyclization Strategies Toward the Synthesis of Zoanthamine Alkaloids

Stabilized 2-amino-1,3-dienes can participate in intramolecular Diels-Alder (IMDA) reactions with pendant dienophiles. We found that these dienes can be readily prepared via standard palladium-mediated coupling reactions and have comparable reactivity to 2-oxodienes. Application of these substrates to the synthesis of tetracyclic model systems representing the ABCE motif of the zoanthamines is presented.

Enantioselective total synthesis of spirofungins A and B

The enantioselective total synthesis of spirofungins A (1) and B (2) is reported in 14 steps over the longest linear sequence. Key steps include the use of thiazolidinethione-mediated aldol reactions to assemble the major fragments and installation of the C1-C6 side chain using a cross metathesis reaction.

Studies on the synthesis of the ABC rings of (+/-)-hexacyclinic acid

A synthesis of the ABC-rings of the polyketide natural product hexacyclinic acid has been achieved. The B-ring was formed first via an intramolecular ester-tethered Diels-Alder reaction, and the A-ring was annulated to this by means of a SmI(2) mediated reductive 5-exo-trig cyclization of a samarium-ketyl radical onto a vinyl group. Finally, the C-ring was closed using olefin metathesis. Interestingly, use of enyne metathesis resulted in the synthesis of a more functionalized 5-membered C-ring in a model system, but an undesired 6-membered C-ring in the actual system. An investigation of this change in selectivity is discussed.

Short synthesis of the C16-C28 polyketide fragment of apoptolidin A aglycone

Starting from (E,E)-1-[(1R)-(phenylethyl)oxy]-2-methylpenta-1,3-diene and triethylsilyl enol ether of butanone rapid access to Koert's advanced C10-C28 polyketide fragment of apoptolidin A is now possible.

A Racemic Synthesis of an AB-Ring System of Hexacyclinic Acid

[structure: see text] An AB-ring system of the polyketide natural product hexacyclinic acid has been synthesized in racemic form. The key steps were an intramolecular Diels-Alder cyclization of an ester tethered 1,3-nonadiene-8-yne, which generated the B-ring, and a samarium diiodide mediated reductive annulation, which was used to form the A-ring.

Reversal of facial selectivity in complex Diels–Alder reactions

A complex Diels-Alder reaction between a semi-cyclic diene with allylic silyloxy substituents and a bromo enone presented an unusual diastereoselectivity: attack of the diene occured on its more hindered face, and this reversal of selectivity was shown to be induced by the presence of a bromo substituent in the dienophile.