Dienes, catalytic hydrogenation Diels-Alder reaction with

For the synthesis of carazostatin (247), the required arylamine 708 was synthesized starting from 1-methoxycyclohexa-l, 3-diene (710) and methyl 2-decynoate (711). The key step in this route is the Diels-Alder cycloaddition of 710 and 711, followed by retro-Diels-Alder reaction with extrusion of ethylene to give 2-heptyl-6-methoxybenzoate (712). Using a three-step sequence, the methoxy-carbonyl group of compound 712 was transformed to the methyl group present in the natural product. 3-Heptyl-3-methylanisole (713) was obtained in 85% overall yield. Finally, the anisole 713 was transformed to the arylamine 708 by nitration and subsequent catalytic hydrogenation. This simple sequence provides the arylamine 708 in six steps and with 26% overall yield (597,598) (Scheme 5.66). 

Ethoxypenta-l, 3-diene underwent the Diels-Alder reaction withp-benzoquinone to give the cis-fused diketone I. Selective catalytic hydrogenation (Ni) of I, followed by reduction with lithium aluminum... 

The most notable chemistry of the biscylopen-tadienyls results from the aromaticity of the cyclopentadienyl rings. This is now far too extensively documented to be described in full but an outline of some of its manifestations is in Fig. 25.14. Ferrocene resists catalytic hydrogenation and does not undergo the typical reactions of conjugated dienes, such as the Diels-Alder reaction. Nor are direct nitration and halogenation possible because of oxidation to the ferricinium ion. However, Friedel-Crafts acylation as well as alkylation and metallation reactions, are readily effected. Indeed, electrophilic substitution of ferrocene occurs with such facility compared to, say, benzene (3 x 10 faster) that some explanation is called for. It has been suggested that. 

Wiseman and coworkers have succeeded in preparing tricyclo[5.3.0.0 ]decane (393), a CioHig hydrocarbon which unlike adamantane is chiral. Their elegantly simple approach entails Diels-Alder addition of cyclobutene to l,4-dihalocyclohexa-l,3-dienes, catalytic hydrogenation of the adduct, reaction with aluminium triiodide, and ultimately di- -butyltin dihydride reduction. 

The in situ Diels-Alder reaction of 4,4-diethylpyrazoline-3,5-dione (from 4,4-diethylpyrazolidine-3,5-dione (26) and lead tetracetate) with 1,3-dienes provides a convenient route to 5,8-dihydropyrazolo[I,2- ]-pyridazine-l, 3-(2// )-diones of type 27, which may be converted to perhy-dropyrazolo[l,2- ]pyridazin-l,3-diones (28) by catalytic hydrogenation over Pd/C [69JOC3I8I, 69LA(724)I50]. Conversion of 28 to 29 by lithium aluminum hydride reduction has been described (72JHC4I). 

The enantiomers of 2-cyclohexy(-2-hydroxy acetic add 12 and their esters are conveniently obtained from the corresponding mandelic adds (or derivatives) by catalytic hydrogenation with a platinum catalyst16 17. The methyl ester has been used for the enantioselectivc protonation of lactone enolates (Section D.2.1.) and the chiral diene prepared analogously to the O-methylmandclic acid derivatives11-13 described in the preceding section in diastereoselective Diels-Alder reactions (Section D. 1.6.1.1.1.). 

Wu and his co-workers reported an experimental and theoretical study on the hydrogen-bond-promoted enantioselective hetero-Diels-Alder reaction (HAD) of Danishefsky s diene 105 with benzaldehyde 106, Scheme 3.37 [52], The reaction was achieved catalytically by a series of a,ct,a, a -tetraaryl-l,3-dioxolane-4,5-dimethanol (TADDOL) derivatives through hydrogen-bonding activation and afforded 2-phenyl-2, 3-dihydro-4H-pyran-4-one 108 in good enantioselectivity. 

Recently, chiral bis-phosphoric acid 77 bearing a new chiral scaffold with triple axial chirality assisted by intramolecular hydrogen-bonding between two phosphoric acid moieties was designed as a new chiral Bronsted acid catalyst by the Terada group [33], Application of this catalyst in the Diels-Alder reaction between substituted acroleins 66 and amido-dienes 76 produced the corresponding cycloadducts 78 with excellent enantioselectivities (Scheme 38.22). In comparison with the mono-phosphoric acid, bis-phosphoric acid 77 showed obviously higher catalytic activity and selectivity. 

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