1- Alkoxy-l,3-dienes

Dihydrothebaine- was originally given the structure [n], which was in accord with most of its chemical properties [3-4] except its failure to condense with benzoquinone or maleic anhydride and its failure to yield a derivative of 14-bromothebainone [iii] on treatment with bromine [5], However, the production of a conjugated diene as final product in a sodium-alcohol or sodium-ammonia reduction is contrary to general experience and examination of the infra-red and ultra-violet absorption spectra of dihydrothebaine-, thebaine, /3-dihydrothebaine, several 1 4-dihydroanisole derivatives, and 1-alkoxy-l 3-dienes led to modification of the structure of dihydrothebaine- to [iv] [6], which structure is more in accord with its properties than is [n], and in particular explains why the hydrogenation of this base proceeds with absorption of only one mole of hydrogen (see Chap. XIV). 

Alkoxy-1,3-dienes and 2-alkoxy-1,3-dienes undergo addition of dichlorocarbene to the more remote double bond157 or to the oxygen-substituted double bond,154 respectively. For example, 1-alkoxy-l, 3-diene 5 gives cyclopropane 6,157 and 2-alkoxy-l, 3-diene 7 gives cyclopropane 8.154... 

Alkoxy-l,3-dienes. a, 8-Unsaturated acetals undergo 1,4-elimination on treatment with this combination of strong bases. Since the alkoxydienes can be de-protonated again by the same base, a one-pot umpolung alkylation is also possible (e.g., starting with 2-alkenyl-l,3-dioxanes). ... 

Pericas and coworkers173 studied the endo selective reactions of 1-alkoxy-l,3-butadienes and 1-alkoxy-l,3-octadienes with maleic anhydride. They found that the trans-2-phenyl-cyclohexan-l-ol and 3-exo-(neopentyloxy)isobornan-l-ol based chiral dienes induced the highest facial selectivities. The relative transition state energies for the formation of the different diastereomers were calculated using semi-empirical methods (AMI). 

In an effort to cause unreactive aldehydes to react in the hetero Diels-Alder reaction Kubler introduced the use of the activated, electron-rich 1-alkoxy-l,3-butadiene. This diene shows increased reactivity and high regioselectivity but only with activated aldehydes. In 1971 Scheeren showed that the potent diene l,l-dimethoxy-3-silyloxy-1,3-butadiene also reacts with aldehydes. The high reactivity of... 

Potassium amide l-Alkoxy-l,3-dien-5-ynes from y-acetylene-j -hydroxyacetals via 0-1-etboxyethylation... 

Titanium tetrachloride d-Alkoxy-a,) -ethylenealdehydes from acetals and 1-siloxy-l,3-dienes... 

Armesto, D., Hoorspool, W.M., Ortiz, M.f., and Romano, S. (1992) Reaction of anions from monoimines of benzil with alkylating agents. Photochemical reactivity of some 4-alkoxy-2-aza-l, 3-dienes. Journal of the Chemical Society, Perkin Transactions 1, 171-175. 

Chiral alkoxy-l,3-cyclohexadienes 1 add to 1,4-naphthoquinone (2) yielding 3 with moderate to very high diastereomcric ratios. The best results (d.r. 97.5 2.5) are achieved for dienes le and lf(l,2 5,6 -di-O-isopropylidene-a-D-glucopyranoside as an auxiliary). Diene Id (2.3,4,6-tetra-0-methyl-/(-D-glucopyranoside as auxiliary) gives a d.r. of only 58.5 41.5. Terpene derivatives as auxiliary alcohols do not work much better d.r. 63 27, 53 47, 64 36 are obtained for la [(-)-borneol], lb [( — )-menthol] and lc [(—)isopinocampheol], respectively18. 

Under solvent-free conditions with microwave irradiation. Moody et al. have improved the hetero Diels-Alder reaction of eneacylamines with l-alkoxy-2-aza-1,3-dienes [67]. A mixture of l-(2-thiazolyl)-l-acetylaminoethylene 54 and the starting 2-aza-l,3-diene 55, irradiated in a GEM Focused Synthesizer at 180 °C for 15 min produced a 64% yield of adduct 56 (Scheme 11.16). Carboxylic acid esters and thiazole rings are tolerated under these reaction conditions (Scheme 11.16). Without microwave irradiation yields were in the range 25 to 42% [67]. 

Chiral (E)-enolethers. A degassed soln. of (5R)-5-cyclohexyl-2-ethenyl-l,3-dioxolan-4-one (2 1 cisjtrans) in THF added to ca. 1 eq. of a suspension of bis(l,5-cycloocta-diene)nickel(0) in the same solvent under N2, stirred until the complex dissolved (10 min), after 3h the resulting rust-coloured precipitate collected, suspended in methylene chloride, treated with MejSiCl, and stirred for 30 min intermediate 7c-allylnickel complex (Y 78%), in benzene treated with DMF and 5 eqs. 1-iodo-propane, irradiated with a sunlamp (GE 275 W Model RSW) for 2,5 h at 10°, stirred for a further 3 h, diluted with pentane to precipitate nickel halide, and stirred for a further 4 h product (Y 82% E/Z 9 1). Subsequent treatment with acetals afforded 2-p-alkoxy-l,3-dioxolan-4-ones with asym. induction, thereby providing an alternative to asym. aldol condensation. F.e. inch reaction with ar. and a,P-ethylene-bromides s. D.J. Krysan, P.B. Mackenzie, J. Am. Chem. Soc. 110, 6273 (1988). 

Alkoxy alkynylcarbene complexes undergo Diels-Alder reactions with neutral and electron-rich dienes [36f, 104] and also with 1-aza- and 2-aza-l,3-butadi-ene derivatives [84a, 105] (Scheme 57). 

The extent of diastereoselectivity observed in the reaction of l-(l-phenylalkoxy)buta-1,3-dienes with indantrione and alloxane is associated with the steric requirements of the alkoxy function in the chiral auxiliary <96SYN105>. 

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