REACTION OF VINYLOGS OF A FISCHER BASE WITH SALICYLALDEHYDES

Article abstract of DOI:10.1007/BF00505693

The reaction of vinylogs of the Fischer base, viz., 1,3,3-trimethyl-2-(3-methyl-2-buten-1-ylidene)indoline, 1,3,3-trimethyl-2-(2-penten-1-ylidene)indoline, 1,3,3-trimethyl-2-(3-phenyl-2-propen-1-ylidene)indoline, and 1,3,3-trimethyl-2-(2-buten-1-ylidene)indoline, with salicylaldehydes commences with displacement by the aromatic o-hydroxy aldehyde of the vinyl part of the dienamine molecule, as a result of which the usual spirobenzopyran is formed.In the case of the first two dienamines the reaction stops at this stage, whereas in the latter two a second molecule of dienamine adds to the initially formed spirobenzopyran at the double bond of the pyran ring to give "dicondensed" spirochromans.