Spiro Dihydroindolizines

H. Gross, Spiro-dihydroindolizine Synthesen und mechanistische Studien eines neuen Photochro-men Systems, Thesis, Universitat des Saarlandes, Saarbriicken (1982). 

A new photochromic system whose structural basis are the spiro-dihydroindolizines was found and studied intensively.It can be prepared easily by different routes and a typical path is shown in Scheme 10. When spirocyclopropenes with the general structure 21 are allowed to react with pyridine or pyridazine derivatives, photochromic [l,8-a]dihydroindolizines 25 (Y = CH or Y = N, respectively) are formed. ... 

Reactions of the easily obtainable spirocyclopropenes 10 with aza-hetero-cycles or azines such as pyridines, pyridazines, quinolines, isoquinolines, azaphe-nanthrenes, and others afford spiro (1,8a) dihydroindolizine 7 in good yields (50-84%) (Scheme 3). The intermediate in this synthesis is the colored betaine 9. Typical dihydroindolizines have been made via this route.1 7 16-18... 

The UV spectra of spiro[l,8a]dihydroindolizine 7 show two typical maxima, one at 240-250 and the other at 360-410 nm. The colored form (betaine) 9, absorbs in the range of 500-700 nm. Similar absorption ranges are observed for the... 

Table 6.2.A Uv-visible data of selected Spiro[l,8a]dihydroindolizines (DHI) 7 prepared by cyclopropene route (a) or pyrazole route (b). Solvent CH2C12/Ether and half life (T ) at...

The reaction of 13, in which the (3-pyridyl)carbonyloxy groups can be either in syn or in anti position, with spiro[cyclopropene-3,9 -fluorene] creates two new stereogenic centers.35 Thus two diastereomers are possible for each the syn- and the anri-isomer which form a pair of C2-symmetrical enantiomers (R,R/S,S) and a Cs- or Cj-symmetrical meso form (R,S) n The resulting calixarenes 14, bearing dihydroindolizine units, were studied as chromogenic compounds ( calixo-chromes ) in quenching experiments not related to their chirality. 

This work has allowed an evaluation of the molar absorptivity of the colored species and the quantum yields of photocoloration and photodecoloration. The examples given include a dihydroindolizine compound, a spiro[benzothiazoline-benzopyran], a 2//-chromcne, a spiro[indoline-benzopyran], and the dimer of the triphenylimidazolyl radical. 

N. A. Garcia, G. Rossbroich, S. E. Braslavsky, H. Durr, and C. Dorweiler, Photoacoustic measurements and MINDO/3 calculations of energy storage by short-lived species the spiro[l,8-a]dihydroindolizine-betaine system, J. Photochem. 37,297-305 (1985). 

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