TRI-N-BUTYLPHOSPHINE-CATALYZED ADDITION AND RING-CLEAVAGE REACTIONS OF CYCLOBUTENONES
TRI-N-BUTYLPHOSPHINE-CATALYZED ADDITION AND RING-CLEAVAGE REACTIONS OF CYCLOBUTENONES
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DOI：
10.1021/jo00078a058
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发表时间：
1993-12-17
影响因子：
3.6
通讯作者：
CAMMERSGOODWIN, A
中科院分区：
文献类型：
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作者：
CAMMERSGOODWIN, A
四元环酮11的近端烷氧基与羰基碳的可逆1，2-加成打开了通过中间体12b到4和6的Grob裂解途径14。这些同步断裂的动力学取决于要断裂的两个键的稳定性。16因此，3在导致2裂解的条件下不愿裂解支持了这种裂解机制，因为当取代基为苯基时，苄基稳定化应该使12b更不稳定。PBu3作为亲核催化剂的另一种方式是通过将膦加成到酮8和酮9上，然后进行类似于上述的Grob裂解，随后从12A的3位失去醇氧得到酰基膦中间体13。结构13可能是失去-质子后得到乙烯基乙烯酮1的来源。16然而，根据以下证据，这条途径不太可能。在环丁烯酮2(85℃)热裂解条件下乙炔基醚和乙醇对乙烯基乙烯酮1的竞争研究中，通过对方案II中对应于14和5b的下场信号的核磁共振积分，乙醇捕获乙烯酮中间体1的速度约为烯基醚17的2倍(k-jki=0.49±0.03)。然而，在膦催化开环的条件下，同样的竞争实验给出了5b，而不是14。此外，乙烯基酮1或酰基膦物种13应该对仲胺的亲核加成反应敏感；但是，在膦催化2开环的条件下，二异丙胺或2，2，6，6-四甲基哌啶的存在不会导致酰胺的形成。因此，离子对13迅速崩溃的12a或12b途径最有可能是膦诱导的环丁烯酮的开环反应。
reversible 1, 2-addition of the proximal alkoxide to the carbonyl carbon of the four-membered ring ketone 11 opens a Grob fragmentation14 pathway to 4 and 6 via intermediate 12b. The kinetics of these synchronous fragmentations depend on the lability of both of the bonds to be broken. 16 Hence, the reluctance of 3 to cleave under conditions that caused the cleavage of 2 supports such a fragmentation mechanism since benzylicstabilization should make 12b more labile when the substituent is phenyl. Another way PBu3 could function as a nucleophilic catalyst is via 1, 2 addition of the phosphine to ketones 8 and 9 followed by a similar Grob fragmentation to the one proposed above with the subsequent loss of alkoxide from the 3 position of 12a to give acylphosphonium intermediate 13. Structure13 could have been a source of vinyl ketene 1 upon loss of the-proton. 16 However, this pathway is unlikely according to the following evidence. In a competition study of ethyl ethynyl ether and ethanol for vinyl ketene 1 under conditions of thermal cleavage of cyclobutenone 2 (85 C), ethanol trapped the ketene intermediate 1 ca. 2X faster (k-Jki= 0.49±0.03) than did the alkynyl ether17 as determined by NMR integration of the downfield signals corresponding to 14 and 5b in Scheme II. However, under conditions of the phosphine-catalyzedring opening of 2, in the presence of the alkynyl ether the same competition experiment gave 5b, but not 14. Furthermore, the vinyl ketene 1 or the acylphosphonium species 13 should have been susceptible to nucleophilic addition by hindered secondary amines; however, the presence of diisopropylamine or 2, 2, 6, 6-tetramethylpiperidine did not result in the formation of amides under conditions of the phosphine catalyzed ring opening of 2. Thus, the pathway via 12a or 12b with rapid collapse of ion pair 13 are most likely forthe phosphine-induced ring cleavage reaction of cyclobutenones.