Propargyl-Claisen rearrangement synthesis

SYNTHESIS OF FURANS AND PYRROLES VIA PROPARGYL CLAISEN REARRANGEMENT... 

Scheme 14 Synthesis of pyrroles via propargyl Claisen rearrangement.

We attempted the synthesis of 1,2-dihydropyridines from propargyl vinyl ethers in an independent study (11JOC2145). In our early experiments, we studied propargyl vinyl ethers 79 with additional alkyl substituents at the vinylic position. The propargyl Claisen rearrangement was effected by catalytic amounts of silver(I) hexafluoroantimonate, and the addition of an amine to the aUenylcarbonyl intermediate was expected to provide the 1,2-dihydropyridine product 80. Unfortunately, the major product was, in aU cases, the 2ff-pyran 81, and the desired dihydropyridine 80 was only formed in yields ranging from 10% to 44% when aniline derivatives were employed (Scheme 27).With aliphatic amines, the formation of 1,2-dihydropyridines was not observed. 

Propargyl Claisen rearrangement AUene synthesis and beyond 13CSR458. Smiles rearrangement in synthetic, mainly, heterocycHc chemistry 13COS935. 

Further variations of the Claisen rearrangement protocol were also utilized for the synthesis of allenic amino acid derivatives. Whereas the Ireland-Claisen rearrangement led to unsatisfactory results [133b], a number of variously substituted a-allenic a-amino acids were prepared by Kazmaier [135] by chelate-controlled Claisen rearrangement of ester enolates (Scheme 18.47). For example, deprotonation of the propargylic ester 147 with 2 equiv. of lithium diisopropylamide and transmetallation with zinc chloride furnished the chelate complex 148, which underwent a highly syn-stereoselective rearrangement to the amino acid derivative 149. 

Synthesis.—Reisch, Mester, and co-workers have made important contributions this year by synthesizing the alkaloids furacridone (34) and ( )-rutacridone (37) for the first time. Regioselective etherification of 1,3-dihydroxy-jV-methylacridone (32 R = H) gave the acetal (33), which furnished furacridone (34) as the major product of acid-catalysed cyclization (Scheme 4). Claisen rearrangements of the 3-allyloxy-acridone (32 R = CH2CH=CH2) and the propargyl derivative (32 R = CH2C=CH) were also studied.18... 

A mercury-free route to allyl vinyl ethers that relies on the Michael addition of allyl alcohols to unsubstituted alkenyl sulfoxides, followed by thermal loss of sulfenic acid and concurrent Claisen rearrangement has been described [145]. This methodology has been applied to the synthesis of isocar-bacyclin [146]. Posner reported an acid-catalyzed protocol that produces conjugated dienoate esters from allylic alcohols and a sulfinyl orthoester [147]. Additionally, the use of propargyl alcoholates and a chloro alkenyl sulfox-... 

The titled reactions are employed for synthesis of benzopyrane derivatives. Thus, the racemic cordiachromene 202 (from the cannabinoid class) was prepared starting from 6-methylhept-5-en-2-one 200 using the Claisen rearrangement of the intermediate propargyl ether 201 in an overall yield of 50% (equation 93) . 

Pregnane Series. Steroid allyl and propargyl enol ethers tindergo the Claisen rearrangement. - Surprisingly, cyanogen bromide reacts with 18-hydroxy-20-dimethylamino steroids to form the corresponding 18,20-epoxy deri-vatives. Additional work has been reported on the synthesis of l8-methyl steroids. ... 

For chirality transfer via a furan ring transfer reaction of tetrahydrobenzofuranyl allenyl ethers and Claiscn rearrangement see refs 675 and 676. The synthesis of cyclopropanes via Claisen rearrangements of propargylic alcohol derivatives is reported in ref 677 and for acetylene Claisen rearrangements of thio derivatives see refs 678 and 679. 

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