Aldehydes ring closure, double with

Furans having a double bond at position 2 can be obtained by a phosphine-initiated cyclization of enyne ketones in the presence of an aldehyde. The reaction may involve the 1,6-addition of the phosphine toward the enyne, ring closure and Wittig reaction of the ylide with the aldehyde <99TL3753>. 

Other new syntheses of the isomers of the dolichodials, chrysomelidial (364A) and dehydroiridodial (364B), have been published. Methyl 2,4-dioxopentanoate and isoprene react together on irradiation to give two products, one of which, 376, underwent ring closure to 377 with titanium dichloride (Scheme 32). Both aldehydes were available by this route because the monoacetal 378 equilibrates on aluminum oxide. Furthermore, the acid of 377 has been resolved as the menthyl ester, making other double-bond isomers available. A somewhat... 

Martel and co-workers 52), by a series of condensation reactions, converted XCIX to C. Pormylation of the double bond, condensation of the resulting unsaturated aldehyde with methyl cyanoacetate, followed by catalytic hydrogenation, saponification, decarboxylation, and reesterification provided Cl. Desacetamidocolchicine (LXII), identical with an authentic specimen, was produced from Cl by ring closure to CII, followed by benzoyl peroxide treatment to give CIII, alkaline hydrolysis to the enolic a-diketone, and subsequent iV-bromosuccinimide treatment. 

With the intermediate 90 possessing all the skeletal carbons with correct stereochemistry in hand, we investigated the final nine-membered ring cyclization along with installation of the C4-C5 double bond. It was anticipated that this ring closure would be accomplished by the intramolecular vinylogous aldol reaction applied to aldehyde 95 (Scheme 12). The aldehyde 95 was prepared from 90 by the oxidation procedure of... 

Luffariella variabilis provided four sesterterpenoid antibiotics (159-162) (117, 118). Manoalide (159) which contains an a,P-unsatu-rated 5-lactol function was without close structural analogy. 160 was an open chain isomer of 159, with -configuration of the C-6,7 double bond which prevents ring closure between the C-24 aldehyde and the... 

There is considerable evidence that this reaction pathway goes through A -piperidine-2-car-boxylic acid, which arises from the a-keto acid by ring closure (the two compounds are in equilibrium with each other). A -Piperidine-2-carboxylic acid can be reduced to pipecolic acid (an excretion product in the rat) but it can also shift its double bond and open the ring by hydrolysis to give an a-amino-6-aldehyde acid which is easily converted to a-aminoadipic acid. (Aminoadipic acid is a rarely occurring amino acid found in proteins from corn, Chapt II-2). 

Substituted 4,5-dihydro-6H-l,3-thiazines (27) are formed in high yields by Michael addition of thioamides, thioureas, or thiocarbamates (25) to the double bond of a 3-unsaturated aldehydes, ketones, or ketols (24) in the presence of boron trifluoride etherate and subsequent spontaneous ring-closure of the resulting intermediate (26). In some instances the products (27) can be converted into the corresponding 6H-l,3-thiazines, c.g. (28), with POCI3 in pyridine or with acid in aprotic solvents. 

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