Heterodienes synthesis

Either dimethyl maleate or dimethyl fumarate participated with 2-cyano-l-azabutadiene derivative (19) in the heterodiene synthesis to stereospecifically form pyridines (20) and (21) (Scheme 14) <95TL(36)8977>. Large rate enhancements were noted using 2.5 M LiNTf2 in acetonitrile. 

Intramolecular heterodiene synthesis used alkyne (22) (Scheme 15) <95B(ECTOC-l)>. 

A pair of papers describe the use of lanthanide triflates, in preference to unstable lithium perchlorate, as catalysts in heterodiene synthesis <95SL233> <95SYN1195>, as was also noted in <95TL(36)8977> and Scheme 14. 

Attempts have also been made338 346 to find a theoretical explanation of the stereo or positional selectivity in the first stage of the heterodiene synthesis, especially in the interaction between 5-ethoxy-4-methyloxazole and asymmetric dienophiles, e.g., /9-acetylacrylic acid and its ethyl ester. ir-Electron density calculations for the diene and dienophile molecules by the HMO method indicate the formation of the 4-acetylpyridine derivative (187) from ethyl /3-acetylacrylate, while the opposite orientation would be expected in the reaction with the free acid, giving a substituted 5-acetylpyridine as the main product. Indeed, 5-ethoxy-4-methyloxazole on condensation with ethyl /3-acetylacrylate affords only 187, while in the condensation with /3-acetylacrylic acid, only 2-methyl-3-hydroxy-5-acetylpyridine (188) is isolated.338 348... 

Spiroketals from a,p-ethyleneoxo compds. Stereospecific heterodiene synthesis... 

Heterodiene synthesis with N-arylazomethines 1,2,3,4-Tetrahydroquinoline ring... 

Under acid catalysis N-arylazomethines participate in heterodiene synthesis as the diene component, rather than as dienophile (as is commonplace). E 0.9 eq. trifluoroacetic acid added to a 0.8 M soln. of N-phenylanil and excess of cyclopentadiene in acetonitrile, and left at room temp, for 2 h - adduct. Y 71%. F.e., and pentacyclics by double heterodiene synthesis s. P.A. Grieco, A. Bahsas, Tetrahedron Letters 29, 5855-8 (1988). 

Stereospecific intramolecular heterodiene synthesis with a,p-ethylenecarhonyl compds. 

Intramolecular heterodiene synthesis with enazo compds. 

Regiospecific intramolecular heterodiene synthesis with in situ-generated selenaldehydes... 

Stereospecific heterodiene synthesis with l,3-dien-2-amines Tetrahydro-4-pyrones from aldehydes... 

Diastereoselective complexation of a chiral [antagonist] ketone with a racemic aluminium Lewis acid catalyst effectively removes one enantiomer of the latter, leaving the uncomplexed antipode free to function as a chiral Lewis acid. E Asym. heterodiene synthesis. 0.1 eq. D-3-bromocamphor, 1.05 eqs. startg. siloxydiene, and benzaldehyde added sequentially to 0.1 eq. of the racemic aluminium complex in degassed methylene chloride at —78°, stirred for 3 h, then subjected to acidic work-up (2S,3S)-product. Y 78% (e.e. 82%, upgraded to > 98% by one recrystallization with ca. 60% recovery). F.e.s. K. Maruoka, H. Yamamoto, J. Am. Chem. Soc. Ill, 789-90 (1989). 

Diene synthesis (s.a. Decarboxylation-diene synthesis Heterodiene synthesis High pressure diene synthesis)... 

N-thioacylamidines 28,637s43 thioacylsilanes 43, 597 thioketones 44,666 Heterodiene synthesis, acid-catalyzed... 

Thioacylsilanes 37, 522s44 heterodiene synthesis with - 43, 597 Thioacylsilanes, unstable precursors 43, 597... 

Heterodiene synthesis. Bis(trimethylsilyl) selenide in toluene treated under argon with ca. 2 eqs. dimethylaluminium chloride in hexane, stirred for 15 h at 100°, the solvent removed carefully under reduced pressure, THF, cyclopentadiene, and fluorenone added sequentially to the residue, and heated under reflux for 16h - cycloadduct. Y 77%. The method is also applicable to the in 5//w-generation of simple dialkyl selenoketones. F.e.s. M. Segi et al.. Tetrahedron Letters 30, 2095-8 (1989). 

Pyrimidinones from l-alkoxy-3-siloxy-2-aza-l,3-dienes and nitriles via heterodiene synthesis... 

Startg. m. treated with 0.1 M pyridine hydrochloride in pyridine at 25° for 12 h product. Y 71%. The method allows the overall transformation of a cw-glycol to a conjugated enal via 0,0 -stannylene derivs. and subsequent Horner (or heterodiene) synthesis. F.e. and with aq. AcOH, also 2-alkylidene-l,5-dialdehydes from 2-alkoxy-3,4-dihydro-2//-pyran ring, s. C. Burnouf et al.. Tetrahedron Letters 29, 5533-4 (1988). 

Review Heterodiene synthesis with a,3-unsaturated carbonyl compounds. 

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