9.1 14-Membered Macrocyclic Lactones
9.1.1 (S)-Zearalenone
The synthesis of zearalenone is an example in which the Stille coupling was
employed for ring closure rather than the apparent macrolactonization. After attentive investigations, eventually the authors ascertained that by using 2–3 mol %
polymer bound Pd(PPh 3 ) 4 catalyst (0.1 mmol/g polymer) in refluxing toluene, the
pivotal intramolecular Stille coupling proceeded quite well in a reproducible
manner (54 %) [78] (Scheme 32).
9.2 16-Membered Macrocyclic Lactones
9.2.1 Elaiolide
The study of copper-promoted Stille reaction has resulted in a number of significant
new developments in the field of cross-coupling reactions. One of the most important discoveries is the use of copper(I) chloride to effect an intramolecular cyclization in the absence of any palladium catalyst [79]. This discovery has led to the
rapid introduction of other copper(I) salts, such as copper(I) thiophene-2-carboxylate (CuTC) introduced by Allred and Liebeskind [80]. CuTC in N-methylpyrrolidinone (NMP) effects very rapid Stille cross-coupling reactions under mild
Scheme 31 Intramolecular HWE reaction in the total synthesis of (+)-rhizoxin D, 123
Synthesis of 12- to 16-Membered-Ring Lactones
395
9.1.1 (S)-Zearalenone
The synthesis of zearalenone is an example in which the Stille coupling was
employed for ring closure rather than the apparent macrolactonization. After attentive investigations, eventually the authors ascertained that by using 2–3 mol %
polymer bound Pd(PPh 3 ) 4 catalyst (0.1 mmol/g polymer) in refluxing toluene, the
pivotal intramolecular Stille coupling proceeded quite well in a reproducible
manner (54 %) [78] (Scheme 32).
9.2 16-Membered Macrocyclic Lactones
9.2.1 Elaiolide
The study of copper-promoted Stille reaction has resulted in a number of significant
new developments in the field of cross-coupling reactions. One of the most important discoveries is the use of copper(I) chloride to effect an intramolecular cyclization in the absence of any palladium catalyst [79]. This discovery has led to the
rapid introduction of other copper(I) salts, such as copper(I) thiophene-2-carboxylate (CuTC) introduced by Allred and Liebeskind [80]. CuTC in N-methylpyrrolidinone (NMP) effects very rapid Stille cross-coupling reactions under mild
Scheme 31 Intramolecular HWE reaction in the total synthesis of (+)-rhizoxin D, 123
Synthesis of 12- to 16-Membered-Ring Lactones
395