Chromenes synthesis

H-pyran synthesis from, 3, 759 bis(trimethylsiloxy) in pyrrole synthesis, 4, 333 chromene synthesis from, 3, 750 cycloaddition reactions with isocyanates, azetidin-2-ones from, 7, 261 dihydropyran synthesis from, 3, 771 fuiyl... 

Benzo[b]furan, 2,3-dihydro-2-hydroxymethyl-4//-chromene synthesis from, 3, 764 Benzo[b]furan, 2,3-dihydro-2-isopropenyl-synthesis, 4, 678, 680... 

Benzofurans, 4, 531-597, 657-712 chroman synthesis from, 3, 785 chromene synthesis from, 3, 753 chromone synthesis from, 3, 828 CNDO, 4, 536... 

Benzopyrylium perchlorate, 3-ethyI-reduction, 3, 662 Benzopyrylium salts C NMR, 3, 590 chromene synthesis from, 3, 756 chromone synthesis from, 3, 829 electrophilic substitution, 2, 49 mass spectra, 3, 618 reactions... 

Homofolic acid, 5,11-methenyl-tetrahydro-biological activity, 3, 327 Homofolic acid, tetrahydro-biological activity, 3, 327 Homoisoflavanones occurrence, 3, 722 thermoisomerization, 3, 722 thermolysis, 3, 728 Homolytic reactions heterocyclic compounds reviews, 1, 74 Homophthalic acid isocoumarins synthesis from, 3, 830 synthesis, 3, 830 Homophthalic anhydride isochroman-l-one synthesis from, 3, 860 20a-Homoporphyrin nomenclature, 1, 30 Homopterocarpin isolation, 4, 998 ( )- D- Homotestosterone synthesis, 1, 453 Homer-Emmons reaction chromene synthesis by, 3, 749 Hortiacine isolation, 3, 149 Hortiamine isolation, 3, 149... 

Phosphonium hexafluorophosphate, benzotriazolyl-N-hydroxytris(dimethylamino)-in peptide synthesis, 5, 728 Phosphonium salts chromene synthesis from, 3, 753 reactions, 1, 531 Phosphonium salts, vinyl-in pyrrole synthesis, 4, 343 Phosphonium ylides in heterocyclic synthesis, 5, 165 Phosphoramide, triethylene-as pharmaceutical, 1, 157 Phosphoramide, triethylenethio-as pharmaceutical, 1, 157 Phosphorane, pentaphenyl-synthesis, 1, 532 Phosphoranes, 1, 527-537 Berry pseudorotation, 1, 529 bonding, 1, 528... 

IH-chromene synthesis from, 3, 766 Quinoline, 4-acetoxy-1,2,3,4-tetrahydro-synthesis... 

Somewhat different type 2-amino-4H-chromene synthesis is represented by the interaction of CH-acidic nitriles 27 with salicylic aldehyde 157 where the phenolic OH and aldehyde groups are present in the same molecule. A conventional mechanistic scheme is represented (Scheme 58), where in the presence of a base nitrile 27 condenses with the aldehyde to give Knoevenagel intermediate 158. Then nucleophilic addition of the OH group leads to iminochromene 159, which then adds a nucleophile (as a rule, the second equivalent of nitrile 27) at position 4 to form 2-amino-4H-chromene 160. 

A particularly useful chromene synthesis involves the thermal rearrangement in an inert solvent of aryl propargyl ethers (33) (62CPB926,63CPB1042) which are conveniently prepared from a phenol and a chloroalkyne. An indication of the ease of cyclization is apparent from the presence of chromene in the ethers prepared in this manner. 

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