2,4-Hexadiene-l,6-diols

The synthesis of isomeric DL-allitol succeeded when the hydroxyl groups in cts,cis-2,4-hexadiene-l,6-diol were protected with benzoyl or mesyl groups. Epoxidation gave the appropriate derivatives of 2,3 4,5-dianhydro-DL-allitol (16%), which were then reduced with lithium aluminum hydride to DL-crt/f/iro-2,5-hexanediol. 

The oxidation of 5-methyl-l,2-dihydro-3/7-pyrazol-3-one with lead tetraacetate produces in situ the corresponding pyrazolone which is trapped by ( , )-2,4-hexadiene-l,6-diol to give the c/.v-cycloadduct 1330. The cis configuration was assigned since hydrogenation affords the same compound which can be prepared alternatively from the cyclohexadiene adduct. 

The first synthesis of racemic LTA4 methyl ester, as a mixture with its cis isomer, was reported by Corey et al. as outlined in Scheme 3.19. Alcohol 45 was used as the synthon for the C-12 portion of the target structure and ( , )-2,4-hexadien-l,6-diol became C-6 to C-11. The functionality in the diol was differentiated by its transformation to 47, which then underwent a Wittig reaction with 46 to yield the 15-carbon alcohol 48. The formation of the mesylate of 48 and the reaction of sulfonium salt 49 with methyl 4-formylbutyrate using LDA as a base is also a difficult step and only modest yields of the target compounds are obtained. ... 

Allylic compounds containing other leaving groups are also reactive toward substitution. Thus alkoxycarbonylation of allylic phosphates is a method of homologation, on which an interesting /3-lactam synthesis is based. Using PhjSiOH as nucleophile in the displacement, 2,4-hexadiene-l,6-diols are synthesizedfrom buta-dienyloxiranes. Desilylation of the products is achieved with KF. 

Substrates of this type were utilized for the synthesis of alditols. Schneider and co-workers prepared from trans and cis 2-buten-1,4-diols 2,3-anhydro-DL-erythritol (54) and -threitol (55) by direct epoxidation with peroxybenzoic acid. This method of epoxide formation failed in the case of 2 ,4 -hexadiene-l,6-diol from the 2Z,4Z isomer the corresponding diepoxide (57) was obtained in a 2% yield only. However, from 1,6-dibromo-and 1,6-dibenzyloxycarbonyloxy-2 ,4 -hexadienes the corresponding derivatives of 2,3 4,5-dianhydro-DL-gal-actitol (56) could be obtained in moderate yields. Compounds of this type are active against some forms of sarcoma. 

Another approach by Naruta and co-workers to the synthesis of 9,9a-dihydro-3H-pyrrolo[l,2-a]indoloquinones was based on photocyclization of a diene and an azidoquinone [23] (Scheme 5). Thus, irradiation of a mixture of two equivalents of 2-azido-5-methoxy-6-methyl-l,4-benzoquinone (40) and one equivalent of doubly protected cis, cfs-2,4-hexadien-l,6-diol (41) gave an in-doloquinone 42 that had the 2,3-trans and 8,9-cis configurations. Selective desilylation followed by mesylation and treatment with DBU at reflux temperature then gave the desired tricyclic compound 43 in 35% overall yield. 

Du Prez and coworkers presented a relevant approach concerning TAD-based chemistry described as a novel click and trans-click strategy (Figure 1.17a). ° The reaction of 4-butyl-l,2,4-triazoline-3,5-dione (BuTAD) with 2,4-hexadiene-l-ol (HDEO) yielded the Diels-Alder adduct TAD-HDEO in an extremely fast, traceless, and irreversible manner. The occurrence of a retro-Diels-Alder reaction can be excluded based on reference experiments with competing 2,4-hexadiene-l,6-diol. Furthermore, an addition-type adduct (TAD-indole) was prepared using a substituted indole, e.g., tryptophan in proteins. To demonstrate the trans-click reactivity. 

Yttrocene complexes catalyze the cascade cyclization/hydrosilylation of trienes to form saturated silylated bicyclic compounds.For example, reaction of the 4-silyloxy-4-vinyl-l,6-hexadiene 69 and phenylsilane catalyzed by Gp 2YMe(THF) at room temperature for 1 h followed by oxidation of crude 70a gave [3.3.0]bicyclic diol 70b in 73% yield over two steps as a single diastereomer (Scheme 18). Selective conversion of 69 to 70a presumably requires initial 1,2-hydrometallation of one of the less-hindered G=G bonds to form alkylyttrium alkene complex II (Scheme 18). Selective S-exo carbometallation of II in preference to -exo carbometallation would form cyclopentyl-methylyttrium complex III (Scheme 18). Gyclization of III via a chairlike transition state would form the strained /r< /75 -fused alkylyttrium complex IIIl, which could undergo silylation to form 70a. 

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