Diene protection

The PTAD-diene protected 22-aldehyde analog has been used by Williams and Eyley to synthesize 24,25-dihydroxy derivatives via an aldol reaction with the tetra-hydropytanyl ether of 3-hydroxy-3-methyl-2-butanone followed by NaBH4/pyridine reduction [scheme (9)] The same starting aldehyde is also a precursor for synthesis of the 25,26-dihydroxy-5,7-diene [scheme (10)] ... 

N-Phenyltriazolinedione [PTD] continues to be a popular probe for the study of reactions of alkenes and dienes. Synthetically, PTC can serve as either a N=N wnthon or a 1,3-diene protecting group. The reaction of thiophene dioxide (150) with PTD (2 eq.) generated bis adduct (ISl) with the loss of SO2. Intermediate (151) decomposed with KOH-MeOH to yield the pyrazine (152) in 84% [94TL(35)2709]. Urazole (153), several steps removed from a PTD cycloaddition, when treated with KOH-EtOH yielded the novel oxazolidinone (154) [94JCS(P1)2335]. The PTD cycloadduct was used as a... 

Barton, D. H. R., A. Gunatilaka, T. Nakanishi, H. Patin, D. A. Widdowson, and B. R. Worth Synthetic Uses of Steroidal Ring B Diene Protection 22,23-Dihydro-ergosterol. J. Chem. Soc. Perkin 11976,821. 

Rearrangement and Chemospecific Epoxidations. PhS02 CHD-epoxide reacts with alkyl lithium reagents to produce various addition adducts and 3-benzenesulfonyl-cyclohexa-2,4-dienol in modest yield. The conversion was considerably improved by exposing the epoxide to LiHMDS to furnish the dienol in quantitative yield (eq 2). The emergent alkoxide can be protected in situ with ferf-butyldimethylsilyl chloride in the same yield. Nucleophilic epoxidation of both dienes, protected and... 

More recently, the tricarbonyliron unit has been applied as a diene protecting group in the total synthesis of amphidinolide... 

Complexation of Natural Products. The Fe(CO)3 moiety can provide a method for diene protection. Steroid interconversions employed tricarbonyl(eigosteryl acetate)iron(O) and tricarbonyl(ergosteryl benzoate)iron(O). Thus treatment of ergosteryl acetate or benzoate with tricarbonyl(4-methoxybenzylideneacetone)iron(O) (preformed by complexation using Fe2(CO)9, or with Fc2(CO)9 in the presence of 4-methoxybenzylideneacetone ), gives the pure desired steroid complex in good yield (60% and 80%, respectively). Nopadiene has been complexed by reaction with Fc2(CO)9 to form an optically active metal complex. ... 

Two years later, Ftirstner et al. developed a synthesis of azepine 277 based on a selective Sharpless asymmetric epoxidation of divinylcarbinol (Scheme 2.60) [89]. The resulting epoxide 272 was then regioselectively opened with allylamine to give the corresponding diene. Protection of the secondary amine with an N-Boc group provided the precursor 275 for RCM. CycUzation proceeded in 94% yield using [Mo]-I catalyst (CH2CI2, 30 min, reflux, 94%). Subsequent conversion of the... 

---