Hydroxy ketones from alkenes

DI- and Tri-anions.—Frequently, the formation of a multi-ion is necessary in order that a specific site in a molecule can be rendered active. This is especially so where that site is less easily lithiated than others within the molecule. Such a case presents itself with the dianions (36), where reaction occurs at the more reactive carbanionic centre to give access to various useful p-hydroxy-sub-stituted compounds from conventional electrophiles. " The requisite dianions can be formed from a-chloro-alcohols and a-chloro-ketones " or alternatively by lithiation of the corresponding mercurial compounds (S ). Since the mercurial compounds can in turn be obtained from an alkene by addition of Hg(OAc)a-H2X, in excellent yield, the method provides a very versatile synthesis of p-hydroxy-compounds from alkenes. The same authors have used the new trianions (38), again generated from a mercury compound by lithium-mercury... 

The 1,3-dipolar addition to terminal alkenes of nitrile oxides, generated from nitromethylene derivatives of bicycloheptane, provides 9,ll-ethano-13,15-isoxazolinoprostanoids, PGH analogs, with alkyl, phenyl, or additional heterocyclic fragment in the oo-chain (461). Chemical transformations of 9,11-ethano-13,15-isoxazolinoprostanoids furnish prostanoids with bifunctional fragments of P-hydroxyketone and a-aminoalcohol in the oo-chain. The reaction of P-hydroxy ketones with methanesulfonyl chloride gives rise to prostanoids with an enone component in the oo-chain. 9,ll-Ethano-16-thiaprostanoids have been prepared, for the first time, by nucleophilic addition of thiols to the polarized double bond in the oo-chain. The 1,3-dipolar addition to terminal alkenes of nitrile oxides, generated from nitromethylene derivatives of bicycloheptane provides 9,ll-ethano-13,15-isoxazolinoprostanoids with an alkyl, phenyl, or additional heterocyclic fragment in the oo-chain (462). 

J-Hydroxy Azides, 1,2-Diazides and a-Azido Ketones From Steroid Alkenes... 

Carbon-Oxygen Bond Formation. CAN is an efficient reagent for the conversion of epoxides into /3-nitrato alcohols. 1,2-cA-Diols can be prepared from alkenes by reaction with CAN/I2 followed by hydrolysis with KOH. Of particular interest is the high-yield synthesis of various a-hydroxy ketones and a-amino ketones from oxiranes and aziridines, respectively. The reactions are operated under mild conditions with the use of NBS and a catalytic amount of CAN as the reagents (eq 25). In another case, N-(silylmethyl)amides can be converted to A-(methoxymethyl)amides by CAN in methanol (eq 26). This chemistry has found application in the removal of electroauxiliaries from peptide substrates. Other CAN-mediated C-0 bondforming reactions include the oxidative rearrangement of aryl cyclobutanes and oxetanes, the conversion of allylic and tertiary benzylic alcohols into their corresponding ethers, and the alkoxylation of cephem sulfoxides at the position a to the ester moiety. 

In these oxidations the use of hydrated CUSO4 is mandatory. In fact, it was found that addition of catalytic amounts of water to the solid oxidant creates a more reactive oxidant for the synthesis of lactones from hydroxyaldehydes (eq lO). Small quantities of aqueous t-butanol added to the solid oxidant permit the direct conversion of alkenes to a-hydroxy ketones anda-cUketones (eq 11). Normally, alkenes are inert to the solid oxidant. These differences are attributed to the formation of a thin aqueous... 

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