Penten-5-olides

Dideoxyhex-2-enono-1,5-lactone derivatives (penten-5-olides) have been prepared (255-258) and employed as starting compounds in synthesis. Thus, Michael addition of benzylhydroxylamine to racemic 6-0-acetyl-2,3,4-trideoxy-D,L-g/ycerohex-2-enono-1,5-lactone (267) took place ster-eoselectively to give the unstable benzyloxyamino-2-pyrone 268, which was readily converted into the /Mactam derivative 269, a precursor of thienamy-cin (259). / -Lactams were also obtained (260) by 1,3-dipolar cycloaddition of nitrone 270 to the unsaturated 1,5-lactone 267, followed by hydrogenoly-sis and subsequent cyclization to the /Mactam 271, having a polyol side-chain at the C-3 position. 

The addition of lithium azide to ferr-butyldimethylsilyloxy-2-penten-4-olides during the synthesis of a 3 -azido-3 -deoxythymidine derivative66 and the diastereoselective addition of benzy-lamine to (R)-4-0-benzyl-4-hydroxy-2-penten-5-olide giving substituted /9-amino acid derivatives67 have also been reported. 

Dialkyl-substituierte 3-Hydroxy-aldehyde ergeben in Gegenwart von uberschussigem Titan(IV)-chlorid mit Malonsaure-diestern in guten Ausbeuten die bisher nicht direkt zu-ganglichen 4,4-disubstituierten 2-Alkoxycarbonyl-2-penten-5-olide ... 

In an attempt to obtain garosamine (99, 3-deoxy-4-C-methyl-3-methylamino-L-ara( mo-pentopyranose) by a totally synthetic method, Dyong and Jersch reacted 4-methyl-3-penten-5-olide (97) with chloramine T-osmium tetraoxide reagent ( oxyamination reagent) and obtained the expected N-tosylaminoalcohol 98 in 50% yield. However, the next steps of the synthesis, N-methylation and... 

Two other a,P-unsaturated 5-lactones (50) and (51), substituted in position 3, were identified in the flavor of Burley tobacco 111). 3-Iso-propyl-2-penten-5-olide (51) and its saturated derivative (52) impart a coconut-like note (555) to tobacco 111). Two doubly unsaturated 5-lactones were identified in peach flavor 567, 568). These are 2,4-pentadien-5-olide (or oc-pyrone) (53) and 2,4-decadien-5-olide (54). The latter, which was also identified in mushrooms 89) has a powerful buttery note. Detailed descriptions of the odors of a-pyrone derivatives are to be found in the literature 476). 

Nickel(O) catalyzed cycloaddition reaction of CO2 with allene has been reported to form 3-methyl-4-methylene-2-pentene-5-olide in 20 % yield [91]. Scheme 5.20 (L = dppe) summarizes the proposed mechanism. Insertion of CO2 into a nickela-cyclopentane intermediate (A, in Scheme 5.20) affords a jt-allyl-nickel carboxylate, from which 3,4-dimethylenepentane-5-olide can be reductively eliminated. 

An important group of cyclic dienophiles are butenolides. Optically active y-substituted butenolides can be prepared from naturally occurring chiral compounds, such as D-mannitol [(5)-5-hy-droxy-2-penten-4-olidc]18, D-ribonolactone [(5)-5-hydroxy-2-penten-4-olide and its derivatives]19 or L-tartaric acid [(5)-2-penten-4-olide known as /i-angelica lactone]20. Chiral butenolides are extremely selective dienophiles in thermal [4 + 2] cycloadditions to acyclic dienes. 

Penten-4-olide (186) combines in the same oxygenative fashion with (170) to assemble the trioxanes (187) and (188) (Equation (26)) <88LA869>. 

Phenylpenta-2,3-dienoic acid, X3.3 Triquinacene-2-carboxylic acid, A 34.11 4-Phenyl-2-penten-4-olide, A"44.11... 

Hydroxymethyl-2-butenolide. 5-Hydroxy-2-penten-4-olide. 5-Hydroxymethyl-3-oxolen-2-one. 2,3-Dideoxy- cero-pent-2-enono-1,4-lactone... 

Hydroxy-2-penten-4-olide, H-164 2-Hydroxy-4-pentenyl glucosinolate, H-190 2-Hydioxypentyl glucosinolate, H-191... 

Only two members of the series of P,y-unsaturated y-lactones are known today 3-buten-4-olide (59a), identified in cocoa 478) and fried onions (555), and 3-penten-4-olide (59b) (a-angelicalactone), identified in white bread (599), soybeans (557) and raisins 488). 

---