Rearrangement salts from alcohol

Salts of o-halogeno-N-heterocyclics, such as 2-fluoro-l-methylpyri-dinium tosylate, and related compounds have been used successfully in a variety of reactions, particularly as agents for esterification, lactoni-zation, and the preparation of amides and thiolic esters They have been used also for the preparation of iodides from alcohols and acid fluorides from the acids as well as for Beckmann rearrangements and reductions, e.g. of a-hydroxyketones to ketones . Various condensed heterocyclic salts have been prepared from l-acylmethyl-2-chloropyridinium salts 2-Dialkylaminopyridinium salts have been used as phase transfer catalysts... 

Secondary or tertiary amides are prepared in good yield from amines and alcohols using an in situ generated N-bromophosphonium salt from the reaction of NBS and PPhs. " Benzylamines are debenzylated by NBS and AIBN and the conversion of amides into carbamates was achieved in a Hofmann rearrangement using NBS/NaOMe, or NBS/DBU/MeOH. ... 

Dinitrocubane (28) has been synthesized by Eaton and co-workers via two routes both starting from cubane-l,4-dicarboxylic acid (25). The first of these routes uses diphenylphos-phoryl azide in the presence of a base and tert-butyl alcohol to effect direct conversion of the carboxylic acid (25) to the tert-butylcarbamate (26). Hydrolysis of (26) with mineral acid, followed by direct oxidation of the diamine (27) with m-CPBA, yields 1,4-diiutrocubane (28). Initial attempts to convert cubane-l,4-dicarboxylic acid (25) to 1,4-diaminocubane (27) via a Curtins rearrangement of the corresponding diacylazide (29) were abandoned due to the extremely explosive nature of the latter. However, subsequent experiments showed that treatment of the acid chloride of cubane-l,4-dicarboxylic acid with trimethylsilyl azide allows the formation of the diisocyanate (30) without prior isolation of the dangerous diacylazide (29) from solution. Oxidation of the diisocyanate (30) to 1,4-dinitrocubane (28) was achieved with dimethyldioxirane in wet acetone. Dimethyldioxirane is also reported to oxidize both the diamine (27) and its hydrochloride salt to 1,4-dinitrocubane (28) in excellent yield. ... 

The use of a cationic aza-Cope rearrangement in concert with a Mannich cyclization has also been applied to the total synthesis of enantiomerically pure (—)-crinine (359) (205). In the event, nucleophilic opening of cyclopentenoxide with the aluminum amide that was formed on reaction of (/ )-a-methylbenzyl-amine and trimethylaluminum gave the amino alcohol 485 together with its (15,25) diastereomer. Although there was essentially no asymmetric induction in this process, the diastereomeric amino alcohols were readily separated by chromatography, and the overall procedure therefore constitutes an efficient means for the preparation of enantiomerically pure 2-amino alcohols from epoxides. When the hydrochloride salt derived from 485 was treated with paraformaldehyde and potassium cyanide, the amino nitrile 486 was formed. Subsequent Swem oxida-... 

The first nonambiguous report of rearrangement of esters derived from propargyl alcohols promoted by silver salts was due to Saucy and coworkers at Hoffmann-La Roche.50 Their observations on the transformation of acetate derived from... 

This reaction based on the petrochemical crude material isobutylene makes the synthetic route to P-ionone (36) substantially shorter and cheaper, especially since the isomeric double bond proves to be advantageous in the subsequent reactions. In addition, i-methylheptenone (37 a) can be converted into methylheptenone (37) by noble metal-catalyzed isomerization. The reaction steps ethynylation (C2 addition), Carroll reaction (C3 addition), ethynylation and partial hydrogenation (C2 addition) lead from methylheptenone (37) via dehydrolinalool (42), pseudoionone (43) and p-ionone (36) to the C15 alcohol p-vinylionol (44). With triphenylphosphine (15), the desired C15 phosphonium salt (13), which is the second important synthetic building block for vitamin A and carotenoids16), is obtained directly from p-vinylionol, by allyl rearrangement. 

Semipinacol rearrangements of diazonium salts derived from 2-aminb alcohols are sometimes called Tlffeneau-Demjanov rearrangements. 

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