ChemInform Abstract: Chemistry of Enol Ethers. Part 86. Diene Condensation of 2‐Trimethylsilyloxy‐1,3‐dienes with α,β‐Unsaturated Aldehydes. 1‐Formyl‐4‐trimethylsilyloxy‐3‐cyclohexenes and 1‐Formyl‐4‐oxocyclohexanes.

Abstract

The regio‐ and the stereoselectivity of the reactions between the 2‐trimethylsilyl‐1,3‐dienes (I), (V) or the tautomeric couple (VIII)/(IX) and acrolein (IIa) or trans‐crotonic aldehyde (IIb) are investigated giving the products shown.

Nonclassical 2,4-diamino-6-(aminomethyl)-5,6,7,8-tetrahydroquinazoline antifolates: synthesis and biological activities

“…This synthetic route, however, was not convenient for large-scale preparation of 23, required for the synthesis of the desired compounds. A search of the literature revealed the synthesis of l-(trimethylsiloxy)-cyclohexene-4-carboxaldehyde (22), 24 which was a suitable precursor to 23. Diels-Alder reaction of the commercially available 2-(trimethylsiloxy)-l,3-butadiene (21) with acrolein was carried out as shown in Scheme 1 and afforded 22 in 64% yield.…”

“…The synthesis of 23 was thus achieved in two steps in an overall yield of 50%, which is a significant improvement over the previous routes. [18][19][20][21][22][23] Cyclocondensation of 23 with dicyandiamide afforded 2,4-diamino-5,6,7,8-tetrahydroquinazoline-6-carboxaldehyde dimethyl acetal (24), which was converted to the protected aldehyde 26, as Although these reaction conditions worked well for the synthesis of compounds 1, 4, 9, 13, and 16, they were unsuccessful for the synthesis of compounds 7, 10, 11, and 18. We reasoned that the failure of the reaction at least in the case of 7 could be attributed to the bulk of Ti(i-PrO)4 which prevented the catalysis. Compound 7 was subsequently synthesized using the less bulky Ti(OEt)4 as the catalyst.…”