✍ Scribed by Kei Takeda; Shin-go Yano; Eiichi Yoshii
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0(26)-Methyl-28,29-bisnor-(+)-kijanolide (23) has been synthesized via aldol reaction of spirotetronate 3 with octahydronaphthalene aldehyde 4 and subsequent macrocyclization of the resulting product. Kijanolide (1) and tetronolide (2), the aglycons of novel macrocyclic antitumor antibiotics kijanimicinla and tetrocarcins, lb have attracted considerable synthetic attention since their subjected immediately after isolation to two-step annulation involving addition of dichlorocerium methoxycarbonylacetylide and MeONa-catalyzed lactonization to afforded spirotetronate 3 in 43% overall yield from 6. Scheme la HC-CCHO TFJSOM &MS 9 5 6 R,= CHO,R,=H b 7 R,=H,RZ=CHO TBS = MOM= 6 R,=CH,OMe,R,=H 'BuMe$i MeOCH, q(a) Yb(fod) (5 mol%), C12C=CHCl, (82%), then a eOCHgZ1, 60 'C (68X, 6/7 = 2O:l); (b) i-Bu2AlH, Et20, 0 'C, 15 min i-Pr2NEF, CHjfC12,_ RT, 2.5 h (95%); (c) Et min; (d) C12CeC=C OOMe (5 equlv), 100 to -45 'C, 75 min 9 N-HF (3 equiv), THF, 0 'C, 5 73% from 8); (e) MeOH (10 equiv), reflux, 1.5 h, then t-i(uMe2SiC1, imidazole, DMF, RT, 15 min (76%).
Hydronaphthalene 4 was synthesized by utilizing Lewis acid catalyzed intramolecular Diels-Alder reaction8 of tetraenal 15, which was prepared from acrolein dimer (11) via a five-step
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A highly ciiasfereoselective synthesis of the top ha/f (4) of kijanolide is described. The key step is fhe exo and diastereoface selective Die/s-Alder reaction of triene 6 and chiral dienophile 6.