4-pentynoic adds

A stmple and general synthesis of 2,2,4,5-tetrasubstituted furan-3(2//)-ones from 4-hydroxyalk-2-ynones and alkyl halides via tandem CO, addition-elimination protocol is described <96S 1431>. Palladiuni-mediated intramolecular cyclization of substituted pentynoic adds offers a new route to y-arylidenebutyrolactones <96TL1429>. The first total synthesis of (-)-goniofupyrone 39 was reported. Constmction of the dioxabicyclo[4.3.0]nonenone skeleton was achieved by tosylation of an allylic hydroxy group, followed by exposure to TBAF-HF <96TL5389>. 

Prepare a stock solution of 4-pentynoic acid by dissolving it at a concentration of 100 mM in 50 percent THF/PBS. Add 6.7 pi of this solution to the protein solution with mixing. 

Propylpentanoic acid (valproic acid) (12) contains no chiral centers, but one of its mammalian metabolites is 2-propyl-4-pentenoic add (14), which has a chiral center at C-2. (S)-2-Propyl-4-pentenoic acid is a much more potent teratogen, at least in some assays, than (R)-2-propyl-4-pentenoic acid [56]. Similar observations have been made for the specific enantiomers of 2-propyl-4-pentynoic acid (15). (S)-2-Propyl-4-penty-noic acid is a much more potent teratogen than (R)-2-propyl-4-pentynoic acid [57]. 

The /3-amino add (S)-ethyl-3-amino-4-pentynoate is a chiral synthon used in the synthesis of xemilofiban hydrochloride, an anti-platelet agent. (R)- and (S)-enanti-omers of ethyl 3-amino-4-pentynoate were obtained in enantiomerically pure form by employing penicillin acylase (Pen G acylase, PGA, Chapter 7, Section 7.5.1) (Figure 13.32) (Topgi, 1999). Both the acylation and deacylation modes were ap-... 

The reaction of potassium salts of 4-pentynoic acids—prepared from the add and KOBu-t or KH—with 1-bromo-l-alkynes affords 6-( )-alkylidene-y-butyrolactonest (Scheme 21). Lithium and sodium carboxylates have proved unsuccessful. Addition of potassium bromide, use of DMSO, and excess 4-pentynoic acid have been found to increase the yield, whereas 1-iodo-l-alkynes lead to the formation of the expected lactone along with major amounts of S-iodo- y methylene-y-butyrolactone. Tri(o-tolyl)phosphine and tri(2-furyl)phosphine can promote an effident transformation. The latter, however, has been found to give the best results. 

---