Reactions of dimethyl .beta.-ketoglutarate with 1,2-dicarbonyl compounds. 6. Reactions of dicarbonyl compounds with dimethyl .beta.-ketoglutarate. 4. Formation of 1:1 adducts

Total synthesis of (.+-.)-4'-demethyl-4-epipodophyllotoxin by insertion-cyclization

“…(10) 5: mp 87-88.5 °C (MeOH); NMR (CDCI3) 6.92 (1 H, s), 6.88 (1 H, s), 5.94 (2 H, s), 4.68 (1 H, dd), 3.44 (2 H, m), 3.29 (3 H, s); mass spiectrum, m/e 340, 338, 336 (M+). Anal.…”

“…1972,94,6190. preparative TLC (EtOAc/hexanes, 3:7, three passes) gave 34% of recovered 13 and 36% of the podophyllotoxin derivative 14;23 one recycle raised the yield of 13 to 48%. Desilylation of ether 14 (excess EtaN-HF, THF, room temperature, 3 da24 gave podophyllotoxin (4) in 89% yield.25 Alternatively, ether 14 was reacted with anhydrous HBr26 (CH2C12-Et20, 0 °C, 8 h). Hydrolysis of the crude 4-epibromo-4'-0-demethyl-podophyllotoxin 15 (CaCOa, aqueous Me2CO, 45 °C, 1 h) gave 47% of white crystalline 4'-0-dimethyl-4-epipodophyllotoxin (3), mp 244-246 °C (MeOH),27 identical in all respects with an authentic sample prepared from natural podophyllotoxin.…”

“…In 1968 Weiss and Edwards reported5 67that bicyclo-[3.3.0]octane-3,7-dione (5) was formed in ~15% yield after hydrolysis and decarboxylation of the tetraester 5b (Scheme I) that collected when 4 and glyoxal were stirred in dilute aqueous solution at pH 5. The endo and exo tetracyclic triketones 6 were later found to accompany 5 in yields of 3.2% and 1.6%, respectively.6,7 The total yield is substantially increased by buffering the reaction mixture at pH 6 where 7b can be isolated in 61% yield;8,9 7b gives a 43% yield of 7 upon hydrolysis-decarboxylation.8 9A12% yield of 5b is also present at pH 6,10 **as are the usual small amounts of 6.…”

A chiralC2axially symmetric naphthalene derivative of a bicyclooctane diketal

“…The Weiss±Cook reaction (Yang-Lau et al, 1976) between acenaphthoquinone, (I), and 1,3-acetonedicarboxylate, (II), led to diketone (III), which was puri®ed by¯ash chromatography (SiO 2 , 9:1 CH 2 Cl 2 /ethyl acetate) and recrystallized to give 62% yield, characterized by 1 H and 13 C NMR and CH analysis (Simion, 1996). Reaction of (III) with two equivalents of (À)-(2R,3R)-butane-2,3diol, (IV) (toluene, re¯ux, PTSA cat.…”

Ilikonapyrone esters, likely defense allomones of the mollusk Onchidium verruculatum

“…cm-l; UV (MeOH) 258 nm (E 6000); lH NMR (CDC13) 6 (a), 9.8 (q),9.7 (q), 9.6 (9, 3 C). The triol 2 (45 mg) was dissolved in dioxane (25 mL).…”