SYNTHESIS OF VITAMIN A AND RELATED COMPOUNDS 



719 



R- CH:CH-C -CH- CH:CH-c'''0CH5 

 OH JC¥. 



CH, 



Ihen KOH (olcohol) 



R- CH: CH- C: CH-CH:CH- C-OH 



xvr 



CH, CM, Q 



R- CH:CH • C: CH -CH :GH-C • CH,- C OCH. 

 XVIIl OH 



CH, 



(CHjlLi 



^ CH, 



R- CH:CH- C: CH-CH:CH-C=0 

 'XVIT 



H3C CHj 



C CH3 CH3 



/ \ H H I H H H I H ,./0 



HjC C • c : C • c: C • C : C • C : C • C-OH 



XEX 



HjC C 



\ / \ 



C CHj 



H2 



Arens and van Dorp Synthesis of Vitamin A Acid 



b. Synthesis 2. The second procedure of van Dorp and Arens^^'^ which 

 results in the formation of vitamin A alcohol, is identical with Method 1 

 up to the formation of the ketone (XVII). This compound is treated with 

 BrMgCiCOC2H5 to produce an acetylenic hydroxy ether of vitamin A 

 (XX). Following a controlled reduction and treatment with hydrochloric 

 acid, vitamin A aldehyde is formed; this can be reduced to vitamin A 

 alcohol by means of aluminum isopropoxide. 



CH5 CHj CH3 CH3 



I Br MgCXOCpH. I I 



R- CH:GH -C: GH-CH:CH- C = ► R • CH : CH - C : CH • CH: CH - C • C : C - OC2H5 



"XVTT 



X£ 



OH 



, , CH3 CH3 



H2(Pd) I I HCI 



— R-CH:CH-C:CH-CH:CH-C- CHtCH-OCaHs 



OH 



(HjO) 



HjC CH3 H3C C H3 



C '^^^ C"j C ^"3 CH3 



/\ hhIhhhIh ,^o ^,, , /\ hhIhhhIh 



HzC c-c:c-c:c-c:c-c:c-C H ^^ — ^ " " HzC C • c : C- c: C • c: C • c: C • CHpOH 



HzC C 



\ / \ 



C CHj 



H? 



H?C C 



\ / \ 



C CHj 



H2 



Synthesis of \'itaniiii A Alcohol ])y the Piocedure of van Dorp and Arens 



(6) Synthesis of Karrer, Jucker, and Schick ^ 



Karrer et aZ.'^^ independently proposed a synthesis of vitamin A some- 

 what similar to the method given in the Arens and van Dorp report. ^'''^■"'' 

 Bromocrotonic acid was reacted with /S-ionone to form the dehydrated ester 



