Side chains, introduction

Fluorination of calcitriol has been performed on the A-ring and on the side chain. Introduction of fluorine atoms on the A-ring of vitamin D3 metabolites has been realised on the positions 2 and 4 [152]. Surprisingly, while introduction of fluorine at C-2 strongly decreases the affinity for the calcitriol receptor... 

Syntheses of a- and p- lapachones and their homologues were carried out by photochemical side chain introduction to quinone. Thus, 1,4-naphthoquinone photochemically reacted with 3-methyl-2-butenal to give 2-(3-methyl-2-butenoyl)-l,4-naphthalenediol (69), regiospecifically. The product (69) was successively treated with acid, with dichloroaluminiun hydride, and finally with iron (III) chloride to derive in turn to cromanon (70), dihydropyran (71), and P-lapachone (35). P-lapachone was easily transformed to a-lapachone (38) by treating with acid. Likewise, from... 

Scheme 8 Approaches to side chain introduction onto glycine or serine/threonine units of small peptides involving an Sml2-mediated reductions step...

Scheme 12 Side chain introduction via xanthate-containing peptides...

Scheme 29 DIB/h-mediated oxidative fS-fragmentation of a furanose derivative followed by side chain introduction...

Side chain introduction by carbopalladation has been utilized in a total synthesis of an-thramycin methyl ether (32) (Scheme Heck reaction of the alkenyl triflate 30 with acrylamide installs the necessary three-carbon chain in moderate yield. The desired alkene geometry and oxidation state are observed in the dienamide 31 with no need for protection of the primary amide. The organopalladium precursor can also be part of the side chain being introduced as illustrated in a synthesis of prostaglandin E2 33. ... 

---