Chromane skeleton

SnCl4 is also superior to 22 SnCl4, and is effective for the enantioselective cyclization of 2-(polyprenyl)phenol derivatives to give polycyclic terpenoids bearing a chroman skeleton.The synthetic utility of 26 SnCl4 is demonstrated by very... 

Electron impact mass spectra of some natural products which possess a 2,2-dimethyl-chroman skeleton have been reported (690MS(2)965, 70OMS(3)94i). The mass spectra of the isomeric a-, /3-, and y-tocopherols have been reported (72MI22204). 

The large-scale pilot plant preparation of the chiral aminochroman antidepressant ebaizotan (also known as NAE-086) was developed by H.J. Federsel and co-workers. The structural features of the target included a disubstituted chroman skeleton, a stereocenter, as well as a non-symmetrical tertiary amine moiety at the C3 position and a secondary carboxamide group at C5. The backbone of the target molecule was constructed using the Perkin condensation of 2-hydroxy-6-methoxybenzaldehyde with hippuric acid under mild conditions. 

The pyran ring required to form the chroman skeleton is generated de novo. 

SCHEME 7.4 Second generation synthesis of robaizotan comprised of 13 steps. Key features are the presence of the fluorine substituent in the starting material, a de novo construction of the chroman skeleton, and a late stage diastereomer resolution. 

Saito, N., Ryoda, A., Nakanishi,W. eta/. (2008) Guanidine-catalysed asymmetric synthesis of 2,2-disubstituted chroman skeletons by intramolecular oxa-Michael addition. European Journal of Organic Chemistry, 2759-2766. 

It may be regarded as the parent of a number of important classes of compounds derived from the y-pyrone skeleton (e.g. flavone, xan-thone) and the important chroman derivatives called the tocopherols (vitamin E). 

An interesting feature of 5-tocopherylacetic acid (51) and its derivatives was their appreciable thermal stability up to 200 °C. In contrast to 5a-substituted tocopherols carrying an electronegative substituent at C-5a, the homopolar C—C bond in the C2-unit at the 5-position of the tocopherol skeleton was shown to be very stable. Thermal decomposition of 51 at temperatures above 250 ° C caused a complete breakdown of the chroman structure, the C3-unit consisting of C-2, C-2a, and C-3 being eliminated as propyne, the side chain as 4,8,12-trimethyltridec-l-ene (Fig. 6.38). Fragmentation... 

The aromatic ring of most chroman-substituted retinoids replaces C-5, C-6, C-7, C-8 and C-18 of the retinoic acid skeleton. However, the aromatic ring in novel nonatetraenoates (73)-(76) appears to replace the cyclohexenyl ring [C-l-C-6] of the retinoid skeleton as does the aromatic ring in acitretin (2). 

The spectroscopic behaviour of the homoisoflavanones resembles very closely that of flavonoids 48). The data clearly indicate the presence of sixteen carbon atoms in the basic skeleton and are consistent only with a 3-benzyl(idene)chroman-4-one structure. This has been proven by synthesis of ( )-5,7-dimethoxy-3(4-methoxybenzylidene)chroman-4-one (33) which was identical with the di-O-methyl derivative of ( )-eucomin (3) (9). 

Neoflavonoids Flavonoids (see) with a 4-phenyl-chroman (neoflavan) skeleton, or a corresponding structure in which the C3 chain (C2, C3, C4) is not cy-clized with oxygen. 

The principal rings in this category are those of pyran, chroman, and flavan. The pyran ring, as has already been stated (p. 19) is the basic skeleton of the sugars in their stable forms. 

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