II. CHEMISTRY AM) INDUSTRIAL PREPARATION 



23 



with the dikctoue XXXI to gi\'e the tetrol XXXV'll wliicli wus selectively 

 hydrogeuated to the coiTespoiidiug polyolefinic tetrol which in turn was 

 dehydrated with pyridine hydrobromide to give ^S-carotene. In each of the 

 three methods the synthetic product was compared with the natural and 

 the two were found identical. Other synthetic variations of the above 

 method are described by Inhoffen and Siemer.^^ 



The synthesis of /3-carotene opened the way for the synthesis of several 

 carotenoids which are not found in nature. Some of these are briefly de- 

 scribed below. 



TABLE VIII 

 Synthetic Carotenoids Unknown in Nature 



XXX VI II /S-Carotenin 



15 15' 



XLII Decapieiio-/3-carotene 



XLIII Decapicno-«i-carotene 



XLI\' Dodecapreno-/3-carofene 



jS-Carotenin (15, IS'-dehydro-^S-carotene) (XXXVIII)^^ jg biologically ac- 

 tive in doses of 10 y. 



(i-Mono-cis-iS-carotene (15, 15'-mono-a.s-/3-carotene) (XXXIX) was syn- 

 thesized from /3-carotenin by selective hydrogenation using the Lindlar 

 catalyst. This carotenoid is unstable and changes slowly on standing in 



