Ring enlargements

Recently the tetrahydrofuran ring of a hemiacetal (45) was enlarged187 by inserting nitrogen from hydrazoic acid to obtain 36 [Eq. (33)]. This method was used for the formation of a 5,6-dihydro-4/f-1,3-oxazine steroid. 

P4nkov4 and M. Tichy, Coll. Czech. Chem. Commun. 39, 1447 (1973). 

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VI,34. RING ENLARGEMENT WITH DIAZOMETHANE CYCLOHEPTANONE FROM CYCLOHEXANONE... 

Reaction of cyclic ketones with diazoraethane leads to ring enlargement. Thus cyctohexanone (I) (1 mol) and diazomethane (1 mol) give /oheptanone (II) in about 60 per cent, yield together with a little epoxide (III) as by product and some cj/cioootanone (IV) resulting from further reaction of cyctoheptanone with diazomethane. ... 

Aldehydes aie conveniendy synthetized by the reaction of boronic esters with dichloromethylhthium or (phenylthio)methoxymethylhthium (336,337). The synthesis of medium-ting boracyclane stmctures by stepwise ring enlargement is based on the reaction of B-methoxyboracycles with chloromethylhthium (338). 

Aziridines also undergo ring enlargement when treatment with thiocyanic acid, cis- and tran5-2,3-Dimethylaziridine (470) with thiocyanic acid gave exclusively trans- and cis-1-amino-4,5-dimethyl-2-thiazoline (471) (72JOC4401). 

Phenyl isocyanate reacts with (82) to form (83) by ring enlargement (74JOC948). Reaction of oxaziridines with diphenylketene proceeds less obviously. Isolated products (84) and (85) contain only the R—N group of the starting material (69TL263). 

Ring enlargement of A-acyl compounds, generally observed with oxaziridines, is observed only occasionally with diaziridines. Under more forced conditions of acylation with acetic anhydride, oxadiazolines like (139) were obtained (76MIP50800). A 4-nitrobenzoyl derivative rearranged at room temperature (76JOC3229). 

In the investigation of a ring enlargement, discrimination was possible between the reaction paths via a 1,3-dipole (142) and a quaternary acyl product (143), precursors of different triazolidones. Exclusive formation of (144) from (141) and phenyl isocyanate decided in favor of the dipolar intermediate (142) (81JOC320). 

A formal ring enlargement of diazirines to five-membered rings is also observed with some hydrazones of ketodiazirines (65CB2509). On attempted preparation of hydrazones (201) from ketodiazirine (200) at 0 C the diazo compounds (202) are plausible intermediates since their transformation to aminotriazoles (203) is known. 

Cyclopropanations by carbenes from chlorodiazirines were observed in several cases, e.g. with the r-butyl compound. Cyclopropanation and stabilization by ring enlargement and by elimination compete in chlorocyclobutyldiazirine photolysis. 

Ring enlargement of benzene derivatives by carbenes generated from diazo compounds (better in the presence of a Rh catalyst) Conversion of aldehydes to ketones by diazo compounds (Schlotterbeck) see also Ptau Planer... 

PFAU - PLATTNER Cyclopropane synthesis DIazoalkane insertion Into olelins wtth lormation of cyclopropanes or ring enlargement ol aromatics to cydoheptatnenes see also lormation ol pyrazoHnes (von Pechman). 

The procedure described is a modification of the directions of Prelog, Frenkiel, Kobelt, and Barman. Cyclodecanone has been prepared by the dehydration of sebacoin followed by catalytic hydrogenation, by the pyrolysis of the thorium or yttrium salt of nonane-1,9-dicarboxylie acid, and by the ring enlargement of cyclononanone, as well as by the reduction of sebacoin. ... 

It is the purpose of this chapter to describe a number of ring enlargement and simultaneous ring enlargement-ring contraction procedures which should be of general use. Recommended illustrative experimental procedures are given. 

To establish the structure of A-homo ketone (3b) Nelson and Schut repeated the TifFeneau ring enlargement of 5a-cholestanone [(Ib) (6a) (6b) -> (7)] and obtained a ketone identical with A-homo ketone (3b). 

In the latter process Dieckmann cyclization of diester (11) using high dilution conditions failed. However, A-homo-5a-cholestan-3-one (5b) identical to the product of diazomethane ring enlargement of (lb) was obtained in 35 % yield when diester (11) was hydrolyzed to the bis-homo diacid and this converted to the thorium salt and pyrolyzed. 

Jones and Price"" therefore concluded that diazomethane ring enlargement of 17j5-hydroxy-5a-androstan-3-one (Ic) proceeds with predominately C3—C4. migration, in contrast to the 5a-cholestane series which differs from (Ic) only in the 17-substituent. 

Ring enlargement of 17jS-hydroxy-5jff-androstan-3-one (12) with diazomethane gives 17j8-hydroxy-A-homo-5j8-androstan-3-one (13) and 17)8-hydroxy-A-homo-5j8-androstan-4-one (14) in a total yield of 72%. 

Acid-Catalyzed Ring Enlargement Using Diazomethane... 

Addition of Dichiorocarbene to Enoi Acetates followed by Solvolytic Ring Enlargement... 

A. Saturated B-Homo Ketones and Hydrocarbons 1. Tiffeneau Ring Enlargement... 

Tiffeneau ring enlargement of 5a-deuterio ketone (59) gives the required 3yS-hydroxy-B-homo-5a-deuteriocholestan-7-one acetate (60). The 6a-bromo-3 -hydroxy-B-homo-5a-deuteriocholestan-7-one acetate (61) obtained by bromination is then treated with lithium bromide in dimethylformamide to give the deuterium free a,j5-unsaturated ketone (62). The loss of deuterium bromide proves that bromination takes place at C-6 and that the carbonyl group must therefore be located at C-7. 

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