Unsaturated alcohols rearrangement

MEYER - SCHUSTER Propargyl alcohol rearrangement Add catalyzed rearrangement of acetylenic alcohols into o, -unsaturated carbonyl derivatives... 

In a formal synthesis of fasicularin, the critical spirocyclic ketone intermediate 183 was obtained by use of the rearrangement reaction of the silyloxy epoxide 182, derived from the unsaturated alcohol 180. Alkene 180 was epoxidized with DMDO to produce epoxy alcohol 181 as a single diastereoisomer, which was transformed into the trimethyl silyl ether derivative 182. Treatment of 182 with HCU resulted in smooth ring-expansion to produce spiro compound 183, which was subsequently elaborated to the desired natural product (Scheme 8.46) [88]. 

Hydration of Massively substituted epoxides in acid can be expected to yield significant amounts of elimination and/or rearrangement products derivable from an intermediate c rbonium ion This expectation is amply fulfilled with 2,3- poxy-2r4J4-trim thylpentane (Eq. 610), which yields in addition to the desired 1,2-diol, an unsaturated alcohol, a ketone, and several other products.61 ... 

Reference to some Russian contributions to the study of dehydration of alcohols and of the pinacoline rearrangement was made by Dolgov (67). This included work on dehydration of unsaturated alcohols. In connection with the current studies of Favorskil s school on vinyl-acetylene derivatives, the work of Zakharova on dehydration of acetyl-enylcarbinols to vinylacetylenes should be mentioned (430). 

The allyl vinyl ether needed for the Claisen rearrangement is an enol ether of an unsaturated aldehyde with an unsaturated alcohol. The two starting materials are themselves derived from a common precursor, making this a most efficient process Heating the enol ether promotes [3,3]-sigmatropic rearrangement propelled by the formation of a carbonyl group. 

CHt—CKOH should both be unstable is a very stri-king proof of the relationship of the ring and double bond and is not in the least vitiated by the fact that the former grouping rearranges to a saturated. ketone,the latter to anm,p-unsaturated alcohol. 

XXXV) and (XXXVI) indicates the occurrence of heterolytic cleavage of the C-3-C-4 bond of the amine (XXXIV). In the presence of an excess of allylzinc bromide, only the amines (XXXIV) and (XXXVI) are isolated. Similar types of reactions have been observed in the reactions of allylic organozinc reagents with unsaturated alcohols (333). The reaction of allylzinc bromide with the branched alcohol (XXXVII) forms both the allylcarbinol (XXXVIII) and the rearranged linear alcohol (XXXIX) (333). 

Tertiary unsaturated alcohols, obtained by the addition of acetylenic or vinylic Grignard reagents to polyhaloacetoncs, react mainly in an S i -type reaction to yield rearranged products... 

The enhanced reactivity of oxiranes due to geometric strain is manifested in their acid- and base-catalyzed reactions, in their rearrangements in the presence of metals and metal compounds, and in their thermal and photocatalytic transformations. These reactions permit the development of new and varied methods of synthesis and the preparation of derivatives that in many cases are difficult to obtain by other routes. The main products of the isomerization reaction are unsaturated alcohols and carbonyl compounds. Great progress has been made in this area of organic chemistry during the past 20 years (The reader is referred to some relevant... 

The formation of the C-3 adduct relies on the fact that the a,P-unsaturated alcoholate, produced, as mentioned above, by attack of the organometallic at the a-site of the a,p-unsaturated carbonyl compound, can rearrange to the enolate resulting from C-3 attack. This isomerization has been more conveniently achieved by raising the temperature to 20 C (Scheme 153, compare d to b Scheme 154 compare c to b)." It has also been performed by adding Hhff A" to the medium (Scheme 152, g Schemes 153 and 154). Otherwise, the C-3 adduct can be obtained directly, and even at -78 C, by using potassium... 

With a phenylsulfonyl group as X (Scheme 41) the intermediate, after rearrangement, will decompose directly to an aldehyde function, which reacts wiA excess alkyllithium to form an unsaturated alcohol. The often efficient transfer of chirality from C-1 of an optically active allylic alcohol to the newly created stereogenic centers at C-3 and/or C-4 is another valuable aspect of the 2,3-Wittig rearrangement which has already found extensive use in natural product synthesis. ... 

In the presence of strong acids such as aqueous H2SO4, carbonyl compounds may react with olefins to form unsaturated alcohols and other products, depending on the reaction conditions. Using H-mordenite as catalyst in a continuous-flow system, 10% conversion of formaldehyde to isoprene was observed at 300° using an isobutylene-to-HCHO (molar) ratio of 3.7. A carbonium ion-type reaction scheme, involving a Prins reaction (1,2) and a subsequent dehydration-rearrangement step... 

Side reactions, P eliminations yielding unsaturated alcohols and dienes, are often observed (Scheme 3) and can even become the dominant reaction [12]. Appropriate choice of reaction conditions is, therefore, required to achieve the selective formation of rearrangement products. 

Diene complexes of Fe form from precursors such as unsaturated alcohols, halides and strained compounds, e.g., cyclopropenes, especially in lieu of unstable dienes . Cis-trans isomerization, hydrogen shifts, skeletal rearrangement and condensation occur, but they can be avoided or minimized by use of reactive metal derivatives, e.g., Fe2(CO)g or benzylidine acetone Fe(CO)3, and mild conditions. 

The most familiar of the sulfonic adds derived from camphor is 10-camphorsulfonic add (44, Reychler s acid45). Both enantiomers are commercially available and convenient procedures exist for their preparation by sulfonation of camphor (ref 46 exemplifies the racemate, but the procedure works equally well for optically active camphor). The free acid is often applied to the resolution of basic compounds such as amines. A detailed review on the use of derivatives of this acid as auxiliaries has been given3. Esters of this add are normally obtained by the reaction of the alcohols with the sulfonyl chloride which is also commerdally available (or readily obtained by the reaction of the free acid with phosphorus pentachloride or thionyl chloride46,48). Such esters with unsaturated alcohols have been used for diastereoselective [1,2] sigma tropic rearrangements (Section D.1.6.3.3.). Allyl esters have been used for enantioselective alkylation reactions, in which camphorsulfonic acid reacts as the chiral leaving group (Section D.1.1.2.2.). 

Unsaturated alcohols to aldehydes. The last example of a NAFlON-catalyzed rearrangement is shown In equation 7. Gaseous allyl alcohols, when passed over the resin at 170-190°C... 

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