Aldehydes contraction

Ring contraction by ozonization of steroids—cyclization of keto aldehydes... 

Nitroso-5//-dibenz[/j,/ azepine (see Section 3.2.1.5.4.1.) in methanolic hydrochloric acid undergoes rearrangement and ring contraction to a mixture of acridine (59%), acridine-9-carbaldehyde (trace), and 2-nitro-5//-dibenz[/ ,/ azepine (3% mp 176-178 C).184 However, in acetone and hydrochloric acid, the aldehyde (57 %) becomes the major product. On thermolysis, (or photolysis in the presence of oxygen), in hydroxylic solvents, the nitroso compound yields mainly acridine (36-76%) together with minor amounts of either 2-nitrodibenzazepine (4-6% by thermolysis) or acridine-9-carbaldehyde (18% by photolysis). However, in non-hydroxylic solvents, e.g. cumene, acridine-9-carbaldehyde (64%) is the major product. 

Ring contractions, such as the Tavorskii reaction on (38), or the cyclopentane aldehyde synthesis on p 374... 

The Prins cyclization can also be coupled with a ring-contraction pinacol rearrangement, as illustrated in Scheme 1.6. This allows a smooth conversion of alkyl-idene-cyclohexane acetal 1-16 to single bond-joined cyclohexane cyclopentane aldehyde 1-17 [le]. 

Increasing use is being made of pyran syntheses based upon [4 + 2] cycloadditions of carbonyl compounds. The appropriate unsaturated aldehyde with ethyl vinyl ether yields 53 with peracids this affords an epoxide that undergoes ring contraction to the aldehyde 54 (Scheme 23) and rhodium catalyzed decarbonylation affords the required 3-alkylfuran with the optical center intact.116 Acetoxybutadiene derivatives add active carbonyl compounds giving pyrans that contract under the influence of acids to give... 

Myocardial infarction, 3 710-711 and blood coagulation, 4 81 Myocardial pacemaker cells, 5 81 Myocardium, 5 79—80 Myoglobin, properties of standard, 3 836t Myosin, role in heart excitation and contraction coupling, 5 81 Myrac aldehyde, 2 278 24 485 Myrascone, 24 571... 

AcetaJdehyde is old. It is not ancient like ethyl alcohol, the essential ingredient in wine, but it owes its discovery to this closely related compound. Scheele first prepared acetaldehyde in 1774 by dehydrogenation of ethyl alcohol. Just as many nicknames get attached to people at infancy, this process generated the name aldehyde. It is a contraction for compounds that are alcohol dehydrogenates. 

Aldol condensation. A misnomer from the contraction of Aldehyde and alcohol, but alcohol is a subsequent step. Aldol condensation involves the reaction of an aldehyde with itself or another aldehyde (dimerizing) in the presence of an alkaline catalyst. The resulting dimer is also an... 

The bromoacetal 95 undergoes ring contraction to the relatively unstable aldehyde 96a in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) or triethyamine (Scheme 9) <1995JME1922>. This aldehyde 96a has been obtained in a one-pot process from anhydrodihydroartemisinin 25 in excellent yield. The stereoselectivity of the reaction with iodine is opposite to that with bromine, and allows the preparation of the isomeric aldehyde 96b, with conservation of the configuration of the starting artemisinin at C-9 <2001TL2125>. 

Another possibility is that these compounds were unsaturated aldehydes that resulted from ring contraction during deamination followed by elimination, during acetylation at 100° in pyridine. 

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