4.4- Diethoxy-2-butenal

Cyclopropenone formation should involve the bisketene 46 and its decarbonylation to the monoketene 47 (a valence tautomer of cyclopropenone 44), since photolysis in protic media like ethanol produces diethoxy diethyl tartrate 45) (meso and d,l). This method was also successful in the case of l,2-diphenyl-3,3-dichloro-cyclo-butene dione (48) giving rise to diphenyl cyclopropenone49 (but as for 44 only a moderate yield was produced) ... 

Both of the stereoisomeric DL-tetroses were obtained21 from 1,1-diethoxy-2-butyn-4-ol (18a). In two steps, involving acetylation of 18a and partial hydrogenation of the triple bond in derivative 18b, cis-4-acetoxy-l,l-diethoxy-2-butene (19) was prepared. ci.s-Hydroxylation of 19 with potassium permanganate, followed by acetylation, led to 20. Hydrolysis (basic, and then acidic) of the protecting groups yielded DL-erythrose (28%). 

The procedure has been extended to the formation of difunctional compounds like 3-methyl-3-butenal diethyl acetal (24%), 1,1-diethoxy-2-butyne (80%), and /3-ethoxyethyl methyl ketone diethyl ketal (92%). A somewhat related reaction is the formation of diethyl acetals of a-formyl esters by treatment of a-bromo esters with zinc and ethyl ortho formate (45 60%). ... 

Unsaturated 3-fonnylphosphonates can be prepared by a Michaelis-Arbuzov reaction that employs l,l-diethoxy-4-bromo-2-butene as the masked formyl group. Reaction with triethyl phosphite at ISS C gives diethyl 4,4-diethoxy-2-butenylphosphonate in 50% yield. Deprotection is accomplished in 98% yield using a cold-saturated aqueous solution of tartaric acid. ... 

NaNH2 is also a basic reagent of choice for dehydrohalogenation. Dehydrohalogenation is easily achieved by treatment of bromo- or chloroaliphatic or bromovinylic compounds with a suspension of NaNH2. For example stearolic acid (ref. 48), 10-undecynoic acid (ref. 49) or diethoxy acetylene (ref. 50) have been so prepared (Fig. 9). In the same conditions phenylacetylene has been obtained from 2-bromostyrene (ref. 51), 2-butyn-l-ol from 3-chloro-2-buten-l-ol (ref. 52) but more drastic conditions are required to prepare cyclohexylpropyne from the corresponding vinyl bromide (ref. 53). 

Dihydrothiophene 1,1-dioxide treated with ozone in abs. ethanol and methylene chloride wtih Dry Ice-methanol cooling and stirring until the soln. becomes blue, treated portionwise with liq. SOg during 10-15 sec., and after 2 min. allowed to warm to room temp, during 8-16 hrs. cis- and trfl -2,6-diethoxy-l,4-oxa-thiane 4,4-dioxide (Y 74-81%) mixed with NH4CI and glacial acetic acid, placed in an oil bath preheated to 125-130°, stirred and refluxed 25-35 min. 4H-1,4-thiazine 1,1-dioxide (Y 69-83%). - By the above ozonolysis process, acetals can be obtained from ethylene derivs. E l-Chloro-4-(o-nitrophenyl)-2-butene and methanol -> o-nitrophenylacetaldehyde dimethyl acetal. Y 84%. F. e. s. W. E. Noland and R. D. DeMaster, Org. Synth. 52, 135 (1972). 

---