a,b-konjuge karbonil bileşikleri sentezleri

Abstract

Organik sentezlerde çıkış bileşikleri olarak çok kullanışlı türler olan asiklik ve siklik a,S-konjuge karbonil bileşiklerinin (enonlar) eldesi zamanımıza değin sortin olmaya devam etmektedir. Günümüz araştırmacıları bir yandan şimdiye değin sentez edilmemiş enonları sentezlemeye uğraşırken diğer taraftan sentez edilmişlerdeki sorunları çözmeye çalışmaktadırlar. Bu sorunlar pahalı çıkış bileşik lerinden multistep reaksiyonlardan ve düşük verimli ürünlerden kaynak lanmaktadır. Bu nedenle yüksek verimli olabildiğince one-pot sentezler önem kazanmaktadır. Enon sentezlerinde çok sayıda organik kimya reaksiyonlarından yararlanmak mümkündür. Çalışmamızda farklı yöntemler kullanarak siklohepten, siklodesen, siklooktadien ve p-pinen olefinlerinden çıkılarak olefinlere karşı gelen a,{5-konjuge karbonil bileşikleri sentez edilmeye çalışılmıştır. Reaksiyonlar sırasında karşılaşılan sorunlar vurgulanmış, her aşamada ele geçen ürünlerin analizleri Gaz Kromatografisi ve înce Tabaka Kromatografisi ile gerçekleştirilmiş, tanımlanmaları ise IR-Spektroskopisi ve zaman zaman ^-NMR spektros- kopisi ile yapılmıştır.

There are few compounds that have more potential and versatility in organic synthesis than cyclic and acyclic a, p- conjugated carbonyl compounds. The aldehydic properties of the ethylenic aldehydes are similar to those of the saturated aldehydes but the presence of the unsaturated linkage gives rise to addition reactions similar to those shown by the olefins. Special reactivity is conferred on the double bond when it is conjugated with the aldehyde group, as in the a, Ş- unsaturated aldehydes; they behave as dienophiles in the Diels-Alder reaction, and react with carbanions in the Michael Reaction. ' The carbon atom in the a-position to the end of the conjugated systems make take part in aldol condensations. CH2-CHO + CH3-CH=CH-CHO > CH2-CH=CH-CH=CH~CHO The a, p- unsaturated aldehydes behave as dienophiles in the Diels- Alder reaction. They react with guanidine to give pyrimidines, hydroxylamine to give isoxazoles, hydrazine to give pyrazoles and hydrazoic acid to give 1,2,3-triazoles. The a, (3- unsaturated ketones exhibit a wide variety of addition reactions, some reagents adding to the. carbonyl group, others adding to the carbon-carbon double bond, whilst some, e.g. Grignard reagents, may add to the conjugated systems with subsequent rearrangement; OH H O R1 III _ ' / H2° 1 1 I R-C-CH=C-R' + R"MgBl > R-C=CH-C-R > r-c-CH^-CH-R" OMgBlR" Halogens and halogen acids add to the double bound in the latter case the halogen atom usually becoming attached to the p- carbon atom. Another important group of addition reactions comprises the Michael addition of compounds, such as malonic, cyanoacetic and acetoacetic acid esters, easily capable of yielding carbanions in the presence of catalytic quantities of alkali. The a,p-unsaturated ketones are also often useful dienophiles in vm o o R-CH=CH-C-R' + CHACOOEt) NaOEt > R-CH-CHz-C-R' CH(C02Et) the Diels-Alder reaction. Yet the available sources of these valuable materials are generally tedious, multistep synthetic routes or expensive commercial suppliers. The starting compounds for the synthesis of a,|3-conjugated carbonyl compounds are alkenes, cycloalkenes, ketones, diesters and several different reaction pathways are available. i- Oxidation of cycloalkenes with/without peroxide catalyzed by transition metal clusters or cobalt naphthenate. (CH2)i | URhcp') ^0^] or CH Co naphthenate. CH t-BuOOH + other products ii- Elimination of water from a-hydroxyketones which were obtained from either alkenes by KMnOA or diesters by Acyloin condensation reactions. COOR iCH2)n I COOR (CH2)a c=o.CH-OH (CH,) 2' a %* vo /" * CH (CH2)n i c=o CH-OAc Pyrciysis; c=o \ (CH2)n_x CH If CH iii- Sensitized photooxygenation or catalytic reaction of silyl enol ethers or allyl enol carbonates derived from ketones by two step reaction. IX LDA ' CH or. R3SiCl A2' a C-OLi -UeLi CH /-CH. catalyst or t ^^ (CH2)n_J I- *.*, sensitizer {CH2) n_ CH \^ C-03İR^ 2. Red/ sol V_c^ other products 0C02^> O iv- Direct bromination of cycloalkanone ketals and subsequent elimination and deketalisation. n /-O^ /^~~C~o (a^)a c=o - > (CH2)a cx } > kCH2)a_i CH-Br 9^ O -HBr, \ \ - > (CH2)B_2 CH ^-CH > {CH2)n_2 CH + products ^ - CH v- Allylic bromination of cyclic olefins with NBS, hydrolysis and oxidation of »-hydroxy alkenes. ?CH."rr<"~~*P* NBS (ru\ \ff hydrolysis (CH2)n S > (CH2> n-1 Z3* > ^ -.CH V ? CH Br X oxidation *^"2'n-l. > V / ^- CH O vi- Direct conversion of parent olefins through an allylic oxidation pathway (one-pot synthesis of the 2-cycloalkenones and other a, p- unsaturated carbonyl compounds by an in situ photo-oxygenation- elimination procedure). (CH2)n \CH + o2 - > «%>« /^ - > \ / \ / base ^-CH2 ^~ ÇH I OOH /-~CH ? ^-CH ^-OT y base ^~-CH I II OOAc o As can be seen in six methods there are several problems to solve in the synthesis of the new and also the known a, p- conjugated carbonyl compounds in moderate yields. In this study cycloalkenes were used as starting compounds and reactions were realized by using method (v) and (vi). The general reaction mechanisms were illustrated as follows (Figure 1.) and the results were summarized as shown in Table 1. The completion of reactions were controlled by gas chromatographic and thin layer chromatographic analysis of samples taken from the reaction mixtures and the products obtained were purified by either classical methods or preparative thin-layer chromatography and preparative gas chromatography techniques. After purification the compounds were identified by their IR spectra and in some cases XH-NMR spectra. In this study two known a, p- conjugated carbonyl compounds were synthesized by different combination of the present literature. P- pinene was firstly obtained in different condition in method II. According to the literature, this enon had been obtained only photolytic reaction starting from p- pinene. xi 1,5-Cyclooctadienon compound was a new a,(3-conjugated carbonyl compound. Whole the products obtained were useful starting compounds for synthesis of several natural products.