Pentadienols

Penicillin V—see Penicillin, phenoxymethyl-, 7, 300 Penicilloate, benzyl-, 7, 303 Penicilloate, D-a-benzyl-a-methyl ester, 7, 303 Penillamine, benzyl-, 7, 303 Penillic acid, benzyl-, 7, 303 Penilloaldehyde, benzyl-, 7, 303 Penilloic acid, benzyl-, 7, 303 Penillonic acid, benzyl-methyl ester, 7, 303 1,2,3,4,6-Pentaazaindene nomenclature, 1, 18 Pentadeca-5,10-dienols synthesis, 1, 428 Pentadienol, tetrachloro-2H-pyran synthesis from, 3, 740 Pentadienonitrile, 5-(l,2-benzoselenazol-3-yl)-X-ray diffraction, 6, 334 Penta-2,4-dienonitrile, 5-(dimethylamino)-2-(2-thienyl)-... 

There are several examples of successful dienol epoxidations (Table 9.2). Catalytic SAE conditions are generally better than stoichiometric for reactive substrates (Entry 1), whilst stoichiometric conditions, on the other hand, are useful for less reactive substrates. Small variations in substrate structure can cause large differences in reactivity and product stability pentadienol could be epoxidized in acceptable yield, whereas hexadienol gave a complex mixture of products (Entries 1, 2). 

The desired intermediates, a pentadienol or a pentenetriol were unknown at the time, but it occurred to me that their synthesis might be accomplished by the partial reduction of a pentenynol or a pentynetriol, the latter being obtained from the reaction of one molecule of acrolein or acrolein dichloride with the Grignard reagent derived from acetylene. The reactions which have been carried out in accordance with this scheme are shown in the accompanying flow sheet. 

Scheme 6.73 Preparation of 3-substituted 2,4-pentadienols 347 and 349 via the symmetrical isopyran 333.

By applying this cycloisomerization protocol, (R)-(-)-coniline was synthesized in 11 steps starting from optically active 2,3-pentadienol [137]. 

The cydization of 3-methoxy(or thio methyl)-3,4-pentadienol with KOtBu also afforded five-membered ring compounds 393-395 [175c],... 

Cleavage of homoallyl ethers 2,4-dienols.1 3,6-Dihydro-2H-pyrans are cleaved to (Z)-2,4-pentadienols by this combination of bases in 35-75% yield. Example ... 

An elegant solution to this problem was devised by Mahler and Pettit,3 who showed that treatment of the (pentadienol)Fe(CO)3 complex (9 equation 4) with acid gave (8), which was isolated as the perchlorate in 50% yield. Hiese two methods (hydride abstraction and dehydroxylation) form the basis for the majority of preparations of dienyliron complexes. 

The lower and higher homologs of the tricycles 30 can also be obtained from 1-alkoxycyclo-pentadienolates and 1-alkoxycycloheptadienolates, the products from the latter lead to bi-cyclo[4.2.1]derivatives by a retro-aldol reaction." ... 

Acid mediated elimination of cyclic (dienyl ether)- and (dienol)Fe(CO)2L complexes leads to the formation of (cyclodienyl)Fe(CO)2L cations (equation 26 and 27) . Protonation of (pentadienol)- or (pentadienyl ether)Fe(CO)3 complexes generates the corresponding (pentadienyl)Fe(CO)3+ cations 167 (Scheme 41). Lillya and coworkers have demonstrated that ionization of the hydroxyl substituent occurs with anchimeric assistance from iron, and that isomerization of the initially generated transoid pentadienyl cation 168 to the more stable cisoid cation occurs with retention of configuration about the Cl—C2 bond . The in situ generated transoid pentadienyl cations may also undergo reaction with heteroatom, hydride or carbon nucleophiles to afford substituted ( , -diene)Fe(CO)3 products (169) . Acyclic (pcntadicnyl)MCp cations (M = Rh, Ir) may be prepared by acidic dehydration of (dienol)MCp complexes. ... 

The trienes were prepared by alcoholysis of (Z)-2,3-dichloro-2-butenedioic anhydride followed by conversion to the acid chloride and reaction with ( )-2,4-pentadienol. 

Cyclization. On treatment with La[N(SiMe3)2]3, a 4-alkynol forms the alkoxide which cyclizes to give 2-methylenetetrahydrofuran the isomer with endocyclic double bond is also formed from 3,4-pentadienol. A modified trisfhexamethyldisilazide) of lanthanum (and of several other rare earth metals) (1) catalyzes intramolecular hydroamina-tion of alkynylamines and the products also undergo hydrosilylation. ... 

Olivomycose (63) also was synthesized from another methyldiol (66), which was biosynthesized by baker s yeast from 2-methyl-5-phenyl-2 ,4 -pentadienol. 

Asymmetric hydroxylation of pentadienols by SLO-1 in eq. (19) has also been studied [262, 263]. It is suggested that the difference in the hydrophobic content between the proximal and distal groups significantly influences the positional specificity of oxygenation. 

We used such an approach in the study of dissociative edep reduction of the p, y-unsaturated alcohols. Specially synthesized deuterated 2,4-pentadienol and its derivatives CH2=CHCH=CHCD2Y, where Y = -OH, -OAc, and -OMe, was taken as a substrate RY [272,273] the deuterium label is necessary to distinguish the 1,5-positions. In contrast to the cases studied earlier (cinnamic alcohol, vitamin A, etc.. Sect. 9.2.2, Natural Polyenes Vitamins A and D, Carotenes, and Porphyrins ), the reaction proceeds here via the symmetric pentadienyl anion [CH2-CH-CH-CH-CD2]. Therefore, two piperylene isomers CH3-CH=CH-CH=CD2 (a) and CH2=CH-CH=CH2-CD2H (h) in the strictly equal amounts could be anticipated as products. However, the preferential formation of one isomer, with the rexp= [a]/ m > 2, was found experimentally. This anomaly was explained by nonequUibrium asymmetric arrangement of anion near the electrode due to the orientation inheritance of the original asynunetric molecule RY. This should lead to the intra-anion... 

Dehydration of (pentadienol)- or (pentadienylether)Fe(GO)3 complexes with a strong acid is the most common method used for the preparation of acyclic (ry -pentadienyljiron cations. It has been demonstrated that ionization of the hydroxyl group occurs with anchimeric assistance from iron, and that isomerization of the initially generated transotd pentadienyl cation to the more stable cisoid cation occurs with retention of configuration about the C1-G2 bond." ... 

Scheme 4-110. Alkylation of (ri -diene)iron complexes. Formation of c/5-pentadienol ethers by addition of triethylamine.

This methodology has been applied to a highly stereoselective biomimetic polyene cyclization using chiral tricarbonyl(ii -l-pentadienol)iron complexes to give rise to franj-decaline (Ti -diene)iron complexes. The transformation represents a potential route to bicyclic sesquiterpenes and tricyclic diterpenes (Scheme 4-191). ... 

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