Isopropenyl - from carboxylic acid esters

Dimethyl sulfoxide Isopropenyl compds. from carboxylic acid esters... 

Isopropenyl esters, conveniently prepared from carboxylic acids and propyne in the presence of the zinc salt, readily effect the acylation of ise-thionic acid and of A-methyltaurine. ... 

As in 0-52 hydrazides and hydroxamic acids can be prepared from carboxylic esters, with hydrazine and hydroxylamine, respectively. Both hydrazine and hydroxylamine react more rapidly than ammonia or primary amines (the alpha effect, p. 351). Imidates RC(=NH)OR give amidines RC(=NH)NH2. Lactones, when treated with ammonia or primary amines, give lactams. Lactams are also produced from y- and 8-amino esters in an internal example of this reaction. Isopropenyl formate is a useful compound for the formylation of primary and secondary amines,897... 

More recently, a similar synthetic strategy was utilized to prepare the Dolastatin 15 via acylation of Meldrum s ester (156). In this work, isopropenyl chloroformate was found to give the best results of several mixed carbonic anhydrides derived from the required starting carboxylic acid when used in the presence of 5 molar equivalents of DMAP. Dolastatin proved to exhibit promising remarkable anticancer properties. 

It is noteworthy that Takeda and coworkers (Ref. 154) recently proposed allyl isopropenyl dicarbonate made from isopropenyl chloroformate and sodium allyl carbonate as a convenient reagent for the preparation of allyl esters of carboxylic acids. Allyl isopropenyl dicarbonate reacts with carboxylic acids in the presence of DMAP under mild neutral conditions to give allyl esters in high yields. Allyl esters which could be deprotected by palladium catalysts are especially useful in the case of unstable compounds under acid or basic conditions, for example O-glycopeptides, penicillin derivatives, etc. 

The electrophilic activation of terminal alkynes by arene-ruthenium(II) catalysts has provided selective access to enol esters. Enol esters are much more reactive than alkyl esters and have been used in a variety of reactions. In the past decade, Dixneuf and co-workers have developed selective approaches to the Markovnikov and antz-Markovnikov addition of carboxylic acids across alkynes by employing different arene-ruthenium(II) catalysts [48,53,54]. Of special interest is the synthesis of AT-Boc-protected 1-alanine isopropenyl ester 110 from N-Boc-l-alanine 108 and propyne 109 mediated by (Ty -cymene)RuCl2(PPh3) complex 107 (Scheme 30) [53]. Addition of the amino acid 108 to the propyne 109 proceeded exclusively in the Markovnikov sense and without accompanying racemization of the substrate. 

The interaction of a alk-l-ene and phosphorus pentachloride to form a complex of the general composition RCH=CH2 2PCl5, now recognized as having the phosphonium salt structure 73, has been known for some time. Very many examples are now known of the decomposition of such complexes with SO2 (or in some cases with P40io ) under controlled conditions when the products are (2-chloroalkyl)phosphonic dichlorides (74) or derivatives thereof. The acids from but-l-ene and pent-l-ene hex-l-ene and hept-1-ene and oct-l-ene and dec-l-ene ° have all been reported. The stability of the initial adducts appears to very considerably, and dehydrochlorination may occur readily if the reaction is carried out with insufficient control. Vinyl and isopropenyl esters of carboxylic... 

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