5.5- Pentenones synthesis

Although the optically active 4-hydroxycyclo-2-pentenone (73a) is a very important starting material of synthesis of prostaglandins, it is not easy to obtain optically pure 73a efficiently. The biphenanthrol host 15 was found to be a good... 

The stereospecific synthesis of 3-oxa-prostanoids is described in the same publication as for 3-thia-prostanoids by K. F. Bernady et aL 63 The principle of this synthesis is also analogous. In that case, the starting material is the corresponding 3-oxa-cyclo-pentenone, 6. Work up, followed by deprotection of the ether, chromatography and saponification gave in 38% yield the free acids of dl-l l-deoxy-3-oxa-PGE, 7 and its Cls-epimer 8, dM 5-epi-l 1 -deoxy-3-oxa-PGEt, in a ratio of approximately 45 55. 

This coupling followed by Nazarov cyclization provides a useful synthesis of cyclo-pentenones. 

Dieneones such as (12) are not particularly easy to synthesise, but any method which might form them under acidic conditions usually gives cyclo-pentenones instead. The aromatic compound (13) was needed for the synthesis of steroid analogues. Disconnecting the bond opposite the carbonyl group gives dienone (14), a Friedel-Crafts product from ether (15) and add chloride (16). 

Hydroxycyclopentenones. In connection with a synthesis of prostaglandins, Stork et al. have developed a general synthesis of 2-alkyl-4-hydroxycyclo-pentenones (4). Base-catalyzed rearrangement of epoxy ketones of type (1)... 

Cyclopentenones. Russian chemists report a new synthesis of 2-cyclo-pentenones by the reaction of alkynes with an acyl tetrafluoroborate, formed in situ from an acyl chloride and silver tetrafluoroborate ... 

In an application from the area of prostaglandin synthesis, the protected 1-iodopropargyl alcohol 164 was reduced to the (Z)-iodoolefin 165, which was subsequently converted via 166 into the functionalized organocuprate reagent 167. The latter then provided the IS-cis-pro-staglandin 168 by a highly stereoselective conjugate addition to the appropriate cyclo-pentenone derivative [111] (Scheme 2-18). 

Reaction of A-protected diethyl aspartate (130) or glutamate (131) with lithium trialkylphosphonoacetate in the presence of DIBALH leads to selective formation of the A-protected y-amino-a,P-unsaturated dicarboxylates (132) as the major product. 3-(Phosphonomethyl)cyclo-pentenones (133) and -hexenones (134) are the products of the reaction of dimethyl succinate and dimethyl glutarate, respectively, with excess dimethyl (lithiomethyl)phosphonate presumably via two phosphonomethylations followed by an intramolecular olefmation. Examples of the many phosphonate olefmation reactions carried out include the synthesis of (2E, 4Z)-4-aminoalkadienoates (135), 2-aryloxy-3-phenylpropenoates (136), and isoxazoles (137). ... 

In an important and valuable extension of the furanoid process it was found that alkyl 2-furancarbinols also could be rearranged effectively to 4-hydroxycyclopentenones (70,71). as illustrated in Scheme 13 for the preparation of the cyclopentenone 62 which serves as precursor to the 3-thiaprostaglandin Ej series. Although this particular example is one in which the allylic hydroxylation process also is inapplicable, we prefer the furancarbinol process for the preparation of the 4-hydroxycyclo-pentenone 63 required for the synthesis of lla-hydroxyprosta-glandins bearing the natural PGj a-chain. 

The PiancateUi rearrangement of 2-furylcarbinols into 4-hydroxycyclo-pentenones New appHcations for an intriguing reaction 13MOL12290. Synthesis of P-halofurans 12THC(27)65. 

Electron-rich alkynes, including ethoxy(trimethylsilyl)-acetylene, reacted with chromium alkenylcarbene conplexes at — 10°C in acetonitrile in the presence of a stoichiometric amount of Ni(cod)2 with warming to 20 °C over 2 h to afford moderate yields (40-49%) of cyclopentenones (eq 10). This completely stereoselective nickel(0)-mediated [3 + 2] cyclization reaction of chromium alkenyl(methoxy)carbene complexes with both electron-withdrawing and electron-donating substituted alkynes provides a general synthesis of substituted 2-cyclo-pentenone derivatives, important synthons for the construction of more complex molecules. ... 

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