# What is the IUPAC preferred name of this tetracyclic natural product?

On page 819 of Vollhardt, Organic Chemistry 7th Ed., the following "subunit of the antibacterial platensimycin" appears. I have attempted to apply von Baeyer and skeletal replacement ('a') nomenclature but am stuck deciding between numberings. Here are some vector drawings:

Is von Baeyer the preferred nomenclature for this molecule? and, if so, what is its correct numbering and preferred IUPAC name?

• Pubchem has the first bridgehead as the spiro carbon, giving a lower index to one of the secondary bridges: 4-oxo-8-oxatetracyclo[7.2.1.1$^{7,10}$.0$^{1,6}$]tridec-2-ene. I don't have access to the 2013 blue book, so I will refrain from writing an answer. (P-23.2.6.2.4 The superscript locants for the secondary bridges must be as low as possible when considered as a set in ascending numerical order, the decision being made at the first point of difference.) – Karsten Theis May 10 at 19:10
• Instead of a von Baeyer name, Chemoffice as well as the usually good ACD/ChemSketch (2017.2.1) prefer a fusion name in this case, i.e. a structure based on 4a,7-methanobenzo[7]annulene. However, I still cannot prove why – when looking into the original IUPAC rules. The resulting name would be 4a,5,6,7,8,9-hexahydro-5,8-epoxy-7,9a-methanobenzo[7]annulen-3(4H)-one. – Loong May 11 at 6:31

The pubchem website has given Platensimycin IUPAC name, $$3$$-$$[3$$-$$[(1S,5S,6R,7S,9S,10S)$$-$$5,9$$-dimethyl-$$4$$-oxo-$$8$$-oxatetracyclo$$[7.2.1.1^{7,10}.0^{1,6}]$$tridec-$$2$$-en-$$5$$-yl]propanoylamino]-$$2,4$$-dihydroxybenzoic acid (see attached picture):

Accordingly, since https://pubchem.ncbi.nlm.nih.gov is usually updating data according to the changes, I believe the name of the cyclic system (without 5,9-dimethyl groups) OP is asking is same as one in the comment by @KarstenTheis (including the correct stereochemistry): $$(1S,5S,6R,7S,9S,10S)$$-$$4$$-oxo-$$8$$-oxatetracyclo$$[7.2.1.1^{7,10}.0^{1,6}]$$tridec-$$2$$-ene (see the blue numbering in the picture).

Late correction: After exchanging few comments with Loong, I realized that the given system should be treated as a chemical compound. Accordingly, the name should have been: $$(1S,5S,6R,7S,9S,10S)$$-$$4$$-oxo-$$8$$-oxatetracyclo$$[7.2.1.1^{7,10}.0^{1,6}]$$tridec-$$2$$-en-$$4$$-one (as suggested by Loong).

• "since pubchem.ncbi.nlm.nih.gov is usually updating data according to the changes" – do we know that they are really doing this? – Loong May 11 at 6:06
• I have seen changing of data on physical properties section. But not sure for everything, though. – Mathew Mahindaratne May 11 at 6:10
• How do we know that the correct name for the moiety as a substituent is the same as its correct name as its own molecule? – holomenicus May 12 at 20:06
• Not exactly the same but related. See, the priority changes going from substituent to a molecule. For example, 4-oxo- for substituent becomes 4-one on the molecule. – Mathew Mahindaratne May 12 at 23:04
• In the full IUPAC name for Platensimycin, why is it "-4-yl]propylamino" instead of "-5-yl]propylamino"? Isn't the tetracyclic part connected to the propylamino part at carbon 5? – holomenicus Jun 13 at 7:13

An elder version of Chemdoodle (8.1.0) suggests a name slightly different from the one in the comment by @KarstenTheis, 8-Oxotetracyclo$$[7.2.1.1^{7,10}.0^{1,6}]$$-tridec-2-3n-4-one.

It may be that I erred while drawing the molecule into the sketcher, hence for a xcheck the screen photo below. The yellowish' spheres indicate Chemdoodle's selection for the current naming -- there are only two atoms of oxygen.