Ynones, /-hydroxy, addition

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>. 

Carbon monoxide rapidly inserts into the carbon—zirconium bond of alkyl- and alkenyl-zirconocene chlorides at low temperature with retention of configuration at carbon to give acylzirconocene chlorides 17 (Scheme 3.5). Acylzirconocene chlorides have found utility in synthesis, as described elsewhere in this volume [17]. Lewis acid catalyzed additions to enones, aldehydes, and imines, yielding a-keto allylic alcohols, a-hydroxy ketones, and a-amino ketones, respectively [18], and palladium-catalyzed addition to alkyl/aryl halides and a,[5-ynones [19] are examples. The acyl complex 18 formed by the insertion of carbon monoxide into dialkyl, alkylaryl, or diaryl zirconocenes may rearrange to a r 2-ketone complex 19 either thermally (particularly when R1 = R2 = Ph) or on addition of a Lewis acid [5,20,21]. The rearrangement proceeds through the less stable... 

Hydroxy-a-diazoketones, generated by addition of the lithium derivatives of a-diazoketones to an aldehyde, give ynones on treatment with boron trifluoride.The addition of copper tetra-alkylborates to ynones occurs in a stereocontrolled cis manner to afford the corresponding enones [equation (29)]. ""... 

Michael addition of ethyl acetoacetate to y-hydroxy ynones RCH(OH)C=CCOR has been found to be followed by cyclization and dehydration to afford fiirans. However, this method cannot be applied to a-methylated acetoacetate and diethyl malonates, with which the cyclization does not occur a mechanistic rationale has been provided. a-Nitroamides (234) have been reported to undergo a base-catalysed condensation with electron-deficient dipolarophiles (235) (EWG = C02Me, CONMc2, CN, S02Ph, COMe) to produce 4,5-dihydroisoxazoles (236) as a result of a multi-step process, where 1,4-addition competes with cycloaddition. The actual mechanism is dependent on the substitution pattern. ... 

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