22 VITAMINS A AND CAROTENES 



^■& 



CH, 



CH=CH-C-CH2-C=CH + 4CjHiMgBr 



OH 



XXX 



CH, CH, CH, 



I I I 



CH = CH-C-CHj-C=CMgBr + 0=C-CH2-CH=CH-CHs-C = 



OMgBr 



XXXI 



CH3 CH, CH, CHj 



r >-CH=CH-C-CH,-C=C-C-CHj-CH=CH-CH,-C-C=C-CH,-C-CH = CH 



I jL I I I I 



^^-^ OH OH OH OH 



XXXII 



CH, CH, CH, CH, 



r-^T-CH=CH-C-CH,-CH=CH-C-CHs-CH=CH-CH,-C-CH = CH-CH,-C-CH=CH 



I jL I I I "1 



— OH OH OH OH 



XXXIII 



p-toluene- 

 sulfonic acid 



CH, CH. ^ CH, CH, 



|'^^'S-CH = CH-C=CH-CH=CH-C=CH-CH=CH-CH=C-CH=CH-CH=C-CH=CH-[j^ 

 ^^'''^ /3-carotene "^Z 



CH, CH, 



CH = CH-C=CH-C=CH r^'S-CH = CH-CH-CH-C=CH 



OH 

 XXXIV XXXV 



In the second synthesis the hthium derivative of the polyvinyl acetylene 

 XXXIV was condensed with the diketone XXXI to give the glycol XXXVI 



CH, CHj CH, CH, 



&CH = CH-C = CH-CsC-C-CHj-CH=CH-CHj-C-C=C-CH=C-CH=CH-,P^ 



XXXVI 



which was selectively hydrogenated by means of a poisoned palladium 

 catalyst (Lindlar)^" to give the corresponding polyolefinic glycol which in 

 turn was dehydrated to give /3-carotene. 



In the third synthesis the Grignard of the carbinol XXXV was condensed 



CH, CH, CH, CH, 



XL ^ ' H I I H I s^ 



r >-CH=CH-C-C-C=C-C-CH,-CH=CH-CH,-C-C=C-C-C-CH=CH-^j^ 



^-^ OH OH OH OH^ -KJ 



XXXVII 



